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JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING https://doi.org/10.1080/13467581.2022.2064471 Types and historical roles of secret gates: a new understanding of the Ming Great Wall based on a digital heritage survey Zhe Li, Xiaolong Tuo and Mengdi Zhang KeyLaboratory of Information Technology for Architectural and Cultural Heritage Approved by the Ministry of Culture and Tourism, School of Architecture, Tianjin University, Tianjin, Nankai District, China ABSTRACT ARTICLE HISTORY Received 1 May 2021 The database of images of the Ming Great Wall, along with on-site investigation and verification, Accepted 3 April 2022 has allowed more than 120 secret gate sites to be located and classified for the first time. Based on typological analyses of the relationship between each type of secret gate’s form and function, KEYWORDS we created a classification system of the Ming Great Wall’s secret gates. By combining traditional Secret gate; the Ming Great historical textual research, site surveys, and GIS micro-terrain analysis, we found that secret gates, Wall; photogrammetry; as a key element, integrate other facility types into a coordinated regional defense system, image database; defense revealing several active and flexible defense modes and more sophisticated planning intentions mechanism than were initially recognized. Finally, based on historical textual research, we found that secret gates played a broad and positive role in political interaction and socio-economic exchanges between the Ming Dynasty and Mongolian tribes, offering a new perspective on the historical function and the “open” or “closed” nature of the Ming Great Wall. Moreover, the methods introduced are likely to be applicable to the examination of other types of cultural route heritage. CONTACT Xiaolong Tuo email@example.com KeyLaboratory© of Information Technology for Architectural and Cultural Heritage Approved by the Ministry of Culture and Tourism, School of Architecture, Tianjin University, Tianjin, Hexi District, China © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the Architectural Institute of Japan, Architectural Institute of Korea and Architectural Society of China. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 Z. LI ET AL. the two sides were never fully interrupted (Deng 1. Introduction 2019), and various types of cultural interaction Various dynasties and political entities throughout occurred (Ha 1996). However, the precise role of the Chinese history, situated in different historical contexts Ming Great Wall in these exchange activities remains and geographical environments, had built great walls. unclear. The research and interpretation perspectives applied According to historical records, in addition to the to understanding the purposes and historical roles of Guan and Kou passes, the Ming Great Wall once such walls are also multiple. For example, walls have contained a lower level of channels distributed been interpreted as boundaries of agricultural and across its length, which Chinese texts as “secret pastoralism resources (Lattimore 1937; Wang 2008), gates” (暗门 or 闇门 ). These secret gates were rela- regulators of political and economic relations (Li tively ubiquitous and more widely distributed than 2017), means of securing the conquest of non-tradi- the Guan and Kou passes (the secret gates were not tional agricultural areas (Di Cosmo 2002; Shelach Lavi necessarily literally “secret”; rather, their secrecy was et al. 2020), etc. The focus of this study is the Great Wall a relative concept that will be summarized in of the Ming Dynasty, and the direct historical reason Chapter 5.4.) for its construction is considered to be the Ming Dynasty’s political and military policy turn in the 16th century (Waldron 1990). The political focus in China 1.1. Secret gates: The lowest level of the Ming shifted to internal affairs, and the border defense strat- Great Wall passageways egy gradually came to depend on the Great Wall defense system (Zhao 2015). Under the influence of A secret gate is a type of passage that was built the blockade formed by the Great Wall, the Ming into a city wall in ancient times. The form and Dynasty and Mongolian tribes maintained necessary location of the gates were kept secret. Such gates political, economic, and resource relationships through were used to send out shock troops when cities customs stations and strategic passes built into the were attacked or besieged as a component of long wall. The physical “open” or “closed” nature of active defense or to send sentries to perform the Ming Great Wall system is most directly reflected in tasks associated with intelligence collection and the geographical spatial distribution of its great passes, transmission. The secret gate was an important “Guan” (关 ), and small passes, “Kou” (口 ). The wall line type of defensive facility in ancient Chinese cities. spans about 5000 kilometers from east to west. Compared with their use in urban defense facil- Relative to the wall’s overall length, the number and ities, secret gates in the Great Wall played an distribution of Guan and Kou passes is limited, sup- important role in the economic and political inter- porting the conservative impression that the wall’s actions that took place in border areas, reflecting the flexibility and openness of the frontier defense length limited exchange between cultural groups. system. However, exchanges of people and goods between Figure 1. Date distribution of ancient books with information related to “secret gates”. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 3 surveys of individual sites and historical materials. 1.2. The gap between the rich historical records and contemporary site research Liu, Cao, and Li (2012) researched secret gates and permanent roadblocks (峡榨 ) in the Ming Great Wall The history of secret gates can be traced back to in Qinghai province, and partly revealed the formal the document Mozi-beitu (墨子 ·备突 ) by Mo Di characteristics of secret gates in the Northwestern (476–390 B.C.), which recorded the design and defense methods associated with secret gates inher- region. These results are mainly based on archae- ited from earlier dynasties (Qin 2006). Many histor- ological reports and historical background interpre- ical documents contain records of secret gates. tation of individual cases. In-depth and systematic Using full-text search, we searched for Ding-xiu research of secret gate sites and their historical role and Unihan (Ding-xiu and Unihan 鼎秀和书同文 ) from the perspective of the Ming Great Wall as a using the keywords “暗门 ” (“secret gate”) and “闇 whole have remained lacking prior to this study. 门 ” (“secret gate” in traditional Chinese writing for The paucity of research on the secret gates reflects secret gate), respectively, and selected records relat- the problems of fragmentation and the loss of detailed ing to defense facilities from the returned items site information owing to the Wall’s large geographical (Figure 1). The earliest document was Mozi-beitu, scale and earlier research efforts’ shortcomings with and usage of these terms was observed in docu- respect to digital information collection and manage- ments up to and including those created in the ment methods. These factors have hindered a compre- Republic of China. The terms’ mentions increased hensive grasp and observation of heritage information sharply after the establishment of the Ming from specific perspectives. Dynasty, and a considerable proportion of the lit- erature’s content was related to the Ming Great Wall. Therefore, secret gates and the corresponding 1.3. Research objective military considerations have a long history and were This paper is focused on the following research topics: an integral aspect of frontier defense during the (1) The general forms of the secret gates in the Ming Ming Dynasty. Great Wall: We sought to determine whether the secret Compared to beacon towers, city walls, passes, gates underwent systematic development in terms of and other facilities found along the Great Wall, their architectural characteristics. By clarifying the secret gates are small in scale and can be easily architectural types based on analyses of the sites’ destroyed or buried. The existing sites are scattered architectural forms and functions, we can make scien- throughout a vast geographical region divided by a tific judgments regarding the gates’ design and asso- complex terrain. Therefore, archaeological investiga- ciated purposes within the complex site environment. tions of the Ming Great Wall Site rarely involve (2) The spatial distribution of the secret gates and secret gates despite the large number of historical the associated defense mechanisms of the Ming Great records that document them. Researchers focus pri- Wall: The secret gates’ locations and forms were related to the local defense environment and were marily on the more common features, such as the often integral to the strategic pass defense. The speci- building types and spatial distribution of the “brick fic strategies and planning concepts at play in the hollow defense tower” (Zhang 2019), site selection secret gates’ placement have not been investigated of beacon towers based on geographic information hitherto. systems (GIS) analyses (Cao, Li, and Zhang 2017; (3) The historical roles that secret gates played in Chen, Du, and Cui et al. 2017), and the rammed the social, economic, and political aspects of the earth technology used to construct the Great Wall frontier area: The secret gate is the most basic (Shen et al., 2018) as well as systematically docu- port of the Ming Dynasty’s northern frontier. As menting the characteristics of the known affiliated such, its historic role may reflect the Great Wall’s key strategic significance from a micro-historical facilities (Li, X.M., 2019). However, few archaeologi- perspective. cal and historical studies relating to the secret gates have been published to date: Li Liya and Sun Chi (2004) found a Z-shaped doorway at the archaeolo- 2. Material and methods gical site of Hongmen Castle (红门马市 ). Based on This study adopted the research perspective of macro- historical documents, they confirmed it to be a cosm and microcosm and must be based on materials secret gate that was used in the horse trade. that prioritize accuracy and comprehensiveness. Shang Heng (2017) made a preliminary study of Therefore, the following material acquisition and the secret gates’ historical function based on field research methods were applied. 4 Z. LI ET AL. Figure 2. Work-flow of basic spatial data acquisition in this study. Figure 3. The distribution of secret gates in the Ming Great Wall. 2.1. Rapid census and type comparison of survey of the location and length of the entire site, heritage information on a super large the collection of 5-meter grid digital elevation geographical scale model (DEM) data within 1 km on both sides of the Wall and 1-meter resolution digital orthophoto From 2005 to 2012, the State Administration of model (DOM) data along with other digital map- Cultural Heritage completed the first nationwide ping results (Chen and Jin et al. 2011). However, survey of the Ming Great Wall relics, including a JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 5 the spatial scale and form of earlier survey results facilities. In theory, digital 3D modeling with cen- are still unable to show the site’s three-dimen- timeter accuracy can be obtained via spatial align- sional details, such as site diseases, facility remains, ment of continuous photogrammetric data and so on. collected using multiple aerial routes and a shoot- Since 2018, our research team has initiated a ing height of about 30–50 meters. On this basis, whole-line digital survey of the Ming Great Wall we conducted preliminary database management with the aim of collecting detailed three-dimen- and image retrieval using the Web GIS platform sional (3D) image information pertaining to the (Figure 2). whole-line ruins and compiled an image database Using the platform, we were able to retrieve quickly of the entire Ming Great Wall line. At present, the and screen high-definition images of the whole wall image database contains ultra-low altitude aerial line, complete the image recognition and location of image data for about 6000 kilometers of the Ming the secret gate sites, and then screen out a total of 82 Great Wall, beacon towers, castles, and other single sites with complete preservation of doorways or Table 1. Architectural types of secret gate sites. 6 Z. LI ET AL. doorway foundations, as well as 25 existing samples of 3.1. Overall distribution of secret gate site Kou passes. Using 3D digital model reconstruction, the The digital survey process revealed that the existing size of each site, including the width and height of the secret gate sites are primarily distributed in the Wall’s inner and outer gate openings, could be obtained with eastern section in Beijing, Tianjin, and Hebei Province. decimeter accuracy. Finally, samples from each site At these sites, the secret gates’ structures mainly involve type were statistically analyzed and compared. brick and stone masonry. In Shanxi Province, secret gate structures of rammed earth covered with bricks are found 2.2. Mutual verification of historical documents sporadically, with a gradual reduction in quantity along and site investigation information the wall from east to west. At the rammed earth wall site in Northwest China, it is almost impossible to find secret Historical documents record the formal characteristics gate sites. As Figure 3 illustrates, historical documents – of the secret gates and related historical events. Using traditional historical textual research methods, we such as ancient maps and local archives – indicate that synthesized the fragmented secret gate information secret gates were widely distributed in the Northwestern and conducted historical interpretation based on the region of the Ming Great Wall. Moreover, secret gate sites actual space of the site to confirm the authenticity of are rapidly disappearing as a result of natural and human the historical information and enhance our under- factors. Owing to the dearth of academic and public standing of the artifacts’ authenticity. knowledge regarding this topic, the secret gates have been overlooked by many protection projects, resulting in a loss of key historical information. 3. Types of secret gate site and their architectural function tendency Using the above research methods and tools, we 3.2. Genealogy of secret gate types adopted whole-line quantitative statistics of secret Using images of the secret gate sites and field gate sites’ characteristics as a starting point to obtain investigations of typical sites, we were able to a holistic and detailed appreciation of the gates’ mate- conduct an architectural typology analysis that rial forms and possible functions and lay an empirical revealed rich architectural forms and genealogical foundation for the subsequent architectural history relationships (Table 1). First, we summarized the research. Figure 4. Width distribution of the outer openings of various types of secret gate sites. JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 7 Figure 5. The height distribution of the outer openings of various types of secret gate sites. core function of each secret gate by categorizing it nomadic tribes during the Ming Dynasty) directly reflect the design intention regarding the efficiency as either a straight-through type or non-straight- and safety of travel through the passage. We cal- through type passage. Each gate was then categor- culated statistics pertaining to the width of the ized as one of six basic types according to specific outer entrance for all samples and found that the streamlined organizational characteristics. Each value distribution range was widest for the arch- basic type had various subtypes with structural top type (type-z1). The value distribution range for and functional differences. The genealogy includes the flat-top type (type-z2) was concentrated in the all secret gate sites found to date. area below 1.05 m, making these smaller than the This genealogy was established based on analyses arch-top type passages (Figure 4). of the sites’ architectural forms and functions, to clarify It was difficult to obtain the height values of the the type and relate it to form and function. Therefore, outer gate openings because the floor surface of the the functional topological relationships in the map do doorways in most sites had been buried by debris not indicate a temporal inheritance and evolution resulting from structural collapse and flood deposits, relationship. or the brick arch of the entrance had fallen such that its current height did not reflect its original appearance. We screened out 27 valid samples that were relatively 3.3. Straight-through type: The most basic form intact. Among these, the height distribution of the of secret gate outer openings of each type of secret gate showed The straight-through type is the key secret gate form. Of no clear regularity (Figure 5). the 82 samples assessed, the straight-through type Overall, the characteristics of flat-top secret gates accounted for the greatest proportion (61%). This reflect the limits of the dimensions of secret gates includes the arch-top type (type-z1) and the flat-top along the Ming Great Wall. Taking sample 6 (type-z2) type, which is supported by a stone beam or (39.328999 N, 114.832913 E) in Figure 4 as an example, slab. the size of the outer gate opening is 0.54 m (width) x 1.09 m (height) while the inner gate opening is 0.83 m (width) x 1.71 m (height). The doorway’s inner dimen- 3.3.1. Scale characteristics of the straight-through sions can accommodate an adult of medium height type standing upright, but they would have had to bend The dimensions of the outer entrance of the secret down to pass through the outer opening. The narrow gate site (here, the outer side refers to the side of shape and small scale of this type of secret gate may be the Great Wall facing the area controlled by 8 Z. LI ET AL. Figure 6. Comparison of the widest and narrowest ‘Kou’ sites. Historical documents indicate that, as a doorway related to the limited span of stone-beam structures form characterized by extreme dimensions, the and reflect the design intention in terms of the safety secret gate form was sometimes adopted for Kou and secrecy of the entrance. passes: “The market-surveillance tower of Shahu Kou (杀虎口 ) is located above the secret gate . . . 3.3.2. Comparing secret gates and Kou passes ”(Wang 1969); “the tower above the pass, towering A high degree of similarity is evident between straight- and majestic, with a secret gate under it”(Da Qing Yi through secret gates and Kou (small) passes, which Tong Zhi). For example, the Shimenzi Kou (石门子 may lead scholars to overlook the secret gate’s parti- 口 ) is a small pass that was built under the jurisdic- cularity as a relatively independent pass level and tion of Leng Kou (冷口 ) (Guo 1987). The width of its architectural form. Therefore, it is necessary to clarify outer doorway is 0.93 m, which is similar in dimen- the secret gate concept by comparing the dimensions sion to a secret gate and contrasts sharply with the of Kou passes and secret gates. widest “Kou” (Figure 6). Table 2. Statistics regarding existing Kou sites of Ming Great Wall. Opening Width Existing Height Number Name Outer Inner Outer Inner Latitude Longitude 1 Shahu Kou 1.67 _ 1.74 _ 40.247375 112.305948 2 Langya Kou 1.42 1.99 1.83 2.84 39.170851 114.376347 3 Zhangjia Kou 1.82 2.57 _ _ 40.844666 114.887206 4 Heidouyu Kou 1.43 _ 2.23 _ 40.333649 115.987117 5 West Qinglong Kou 1.19 _ _ _ 40.335578 115.991719 6 Zhuangdao Kou 2.34 2.94 3.11 4.36 40.414575 116.326997 7 Xiaochangyu Kou 2.31 2.85 2.29 3.55 40.418059 116.352601 8 Dazhenyu Kou 4.37 4.94 3.77 5.03 40.454924 116.430691 9 Mutianyu Kou 2.21 2.22 3.33 3.23 40.429973 116.565878 10 Taochun Kou 1.46 1.46 2.65 2.75 40.680988 117.227141 11 Zhuanduo Kou 1.28 1.59 2.28 3.30 40.676798 117.232032 12 Shaling Kou 0.92 1.01 2.18 2.20 40.67615 117.238869 13 Houchuan Kou 1.26 1.42 2.40 3.48 40.677692 117.249689 14 Bailing Kou 1.75 2.10 3.09 2.98 40.672155 117.342848 15 Daobanling Kou 2.56 2.82 2.86 3.80 40.685343 117.40383 16 Wudaoling Watergate 1.81 _ 2.13 _ 40.683797 117.417798 17 Hanerling Kou 2.19 2.34 _ _ 40.668145 117.496102 18 Qingshan Kou 2.55 2.39 4.51 4.59 40.408318 118.54605 19 Baidaozi Kou 1.36 1.38 2.36 2.37 40.190993 118.750762 20 Shimenzi Kou 0.93 1.31 1.82 2.14 40.198244 118.773333 21 Liujia Kou 2.92 4.22 4.16 5.97 40.141316 118.934281 22 Chongyu Kou 1.99 2.09 _ 3.23 40.092914 119.0868 23 Ganjian Kou 1.81 2.27 _ _ 40.10158 119.121089 24 Luohandong Kou 3.31 3.31 3.63 3.28 40.154343 119.238081 25 Wuming Kou 1.86 1.84 _ 2.29 40.192774 119.743319 Table 3. Comparison of width distribution characteristics of outer openings between straight-through secret gates and Kou sites. Pass Type Number of Samples Maximum (m) Minimum (m) Median (m) Mean Value (m) Standard Deviation Secret Gate 82 2.38 0.50 1.03 1.15 0.45 Straight-Through (Arch-top type) 39 2.38 0.73 1.24 1.34 0.43 Straight-Through (Flat-top type) 12 1.03 0.54 0.77 0.78 0.15 Kou 25 4.37 0.92 1.81 1.95 0.78 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 9 Figure 7. Secret gate site with blocking wall inside the doorway in Tianyun mountain, Beijing. Figure 8. The Tumen site at Jieling Kou and a reproduction image. We selected 25 samples of Kou sites with rela- gates and Kou passes in terms of outer doorway tively complete doorways from the Ming Great Wall width revealed that the values for Kou passes were image database (Table 2). Comparison of the med- significantly higher than those for straight-through ian and mean values of the straight-through secret secret gates (either type-z1 or type-z2) (Table 3). 10 Z. LI ET AL. Overall, the above analysis indicates that the 119.232475 E) at the Jieling Kou (界岭口 ) section. secret gate is a relatively independent item in the The false wall does not bear the weight of the Ming Great Wall’s doorway system, but their narrow arched top of the doorway but is integrated with and secretive doorway form was also used by some the outer surface of the city wall and has the same small passes. masonry texture. Before it was broken, this secret gate could not be identified from the outside of the wall (Figure 8). 3.4. Secret gate type with specific function This type of secret gate has a long history. Du tendency You (杜佑 735–812 A.D.) described this form of secret gate as follows: “ . . . cutting tunnels in the The construction and planning of frontier passes city wall from the inner side until just 15–20 cm of including secret gates, required serious considera- packed earth is left to prevent penetration of the tion regarding the conflicting needs of trafficability outer layer of the wall. In the middle of the night, and security. To balance this requirement with vary- or at the beginning of the enemy’s arrival such ing terrain conditions, two main groups of design that their camp is incomplete, the elite cavalry features that are more complex than the straight- leaps out of the Tumen to attack the enemy unpre- through type were adopted in some secret gates: pared” (Mo Di, 2006). Tumen (突门 ), meaning lit- (1) wall-climbing-steps, defense-platforms, and erally “the gate used to launch a sudden attack” is watchtowers to maintain the trafficability of the a special form of secret gate. The remains of such straight-through doorway and strengthen the gates are particularly rare across the Great Wall, defense of the entrance and the interior (type-Z3 perhaps because they were designed specifically in Table 1) and (2) set changes in the horizontal for wartime rather than daily life, limiting their direction (type-WZ and NZ in Table 1) or vertical application. The secret gate of Jieling Kou (界岭 direction (type-DL in Table 1) of the passage’s tra- 口 ) offers precious physical evidence of the ancient jectory to form a non-straight-through secret gate, Tumen defense facility. thus diminishing trafficability and strengthening the doorway’s military control. 3.5. The construction time sequence relationship The non-straight-through secret gate type includes between the secret gate and the wall lines a special form of blocked doorway (type-FD in Table 1). For example, the secret gate in the wall section of The temporal sequence of construction between the Tianyun mountain (天云山 ) has a blocking wall inside secret gate and wall lines and other facilities reflects a straight-through doorway. The defender can climb to the functional closeness between the secret gates and the top of the blocking wall using the inner steps and the entire defense system and whether the secret gate use a ladder to descend the wall to the outside. participated in the entire spatial and functional plan- Alternatively, under the cover of the blocking wall, ning process of the Great Wall’s defense system. The they can attack any enemies who enter through the limited information about the secret gates’ construc- doorway. This design facilitates one-way access to the tion time (Table 4) indicates that they were generally inside of the wall (Figure 7). constructed at the same time as other facilities, such as Our analysis also revealed a secret gate form with the wall, defense tower, guard room, water gate, and an outside entrance that was completely concealed. so on. Therefore, the time taken to create the secret We found a half-brick-thick false wall obscuring the gates may be estimated based on the large-scale con- outside entrance of a secret gate (40.154803 N, struction time of the walls in each section. During the Table 4. Construction information of secret gate in the Ming Great Wall. Water Water Wall Pass Defense tower Guard room Secret Gate Gate opening Time District (边墙 ) (关口 ) (敌台 ) (铺屋 ) (暗门) (水门 ) (水口 ) Documentation sources 1574.A.D. Yansui 671 Li 1 - 83 - 45 (Zhao, Ma, and Lu 1542) (万历二年 ) 1533 A.D. Shanxi 180Li 3 43 55 5 - 12 (Hu 1962) (嘉靖十二年 ) 1548.A.D. Shanxi 140Li - 197 - 3 1 1 (Sun and Li 2012) (嘉靖二十七年 ) 1545.A.D. Shanxi 90Li - 44 62 1 - 1 (Jue and Chu 1734) (嘉靖二十四年 ) 1547.A.D. Xuanfu 719Li - 719 719 60 - 9 (Wang, Wang, and Wu 1743) (嘉靖二十六年 ) 1549.A.D Xuanfu 169Li - 92 276 2 - 3 (Wang, Wang, and Wu 1743) (嘉靖二十八年 ) JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 11 early Ming period, the northern frontier facilities larger doorways, to allow the passage of cavalry. mainly consisted of strategic fortresses, beacon towers, In the wall section of Ningxia, located in the flat trenches, and walls near the passes (Li 2019). Gobi desert, Li Shiao (李士翱 1488–1562 A.D.) sug- According to the results retrieved from the database gested that a barbican entrance (瓮城 ) be con- of ancient Chinese books (mentioned in Section 1.2), structed with a new secret gate outside the the earliest record reads as follows: “in 1430 A.D.(宣德 original secret gate to strengthen protection, and 五年 ), the main pass castle and two blockade walls introduced the usage: were built . . . two rivers converge and pass through “First put down the gate plate of the old secret the secret gate . . . ” (Chu 1780). The emergence of the gate, then fill the Barbican ground with tie ji li (铁蒺 secret gate in the Ming Dynasty’s northern fortifica - 藜 ; an iron ball with spikes), and lift the new secret tions may have begun with the construction of local gate open . . . Seeing that the gate has been blockade walls at strategic passes. opened, the enemy will certainly not continue to From the Chenghua period (成化年间 1465–1487 A. attack the wall, but rush into the secret gate. When D.), Ningxia ( ), Yansui ( ), Datong ( ) and more than a dozen cavalry rushed in, the garrison other western regions took the lead in building contin- immediately put down all the gate plates . . . .” (Li uous walls on a large scale. The continuous walls in the 1962.) eastern four military districts (in which 94% of the sites The secret gate was evidently basically synchro- sample in this study are located) were built between nized with the wall line in the construction sequence 1551 and 1555 A.D. (i.e., during the Jiajing period ) and was a long-standing indispensable facility in the (Liu 1997). Therefore, secret gates may appear in large Ming Great Wall system. It was not a product of tem- numbers simultaneously with the gradual construction porary and unofficial construction and later transfor- of continuous walls after the Chenghua period, reaching mation. Of course, owing to the limitations of the their climax during the Jiajing period. historical materials, it is impossible to observe the As it was widely used in defense operations, the temporal and spatial distribution regularity and regio- form and function of the secret door would also be nal differences of secret gate construction activities, changed and improved according to the actual which remain a topic for future research. combat experience and regional characteristics. For example, the appearance of type DL (Table 1) 4. The role of secret gates in local defense should be later than the form of secret gate set system of the Ming Great Wall on the wall. The construction of hollow brick defense towers began in 1569 A.D. (Fan 2010). Qi Above, the basic functions of the secret gate were Jiguang (戚继光 1528–1588 A.D.), the founder of analyzed based on architectural scale. In this section, the hollow defense tower, would adjust the secret the analytical perspective shifted to the site’s regional gates’ positions based on practical experience: environment and found that a positive supportive and “The secret gate opened under the defense cooperative relationship operated between the secret tower is weak in defense, while the construction gates and other facilities (for example, branch walls, of the wall builders is rough. I worried that their defense towers, passes. etc.), indicating the deep inte- engineering construction does not follow the rules gration of secret gates and regional defense planning or is not solid. It seems safer that the gate is moved intentions. from the foundation up to the outer wall of the In the section that follows, we discuss and sum- defense tower with a ladder placed outside, which marize typical applications of secret gates accord- could be take back when the enemy attacks.” (Qi ing to trafficability based on slope analysis. Basic 1962) terrain data with sub-meter accuracy were This may be regarded as the beginning of type DL. obtained via aerial photogrammetry at a relative The historical records suggest that some secret height of about 200 meters. The impacts of slope gates in the western sections of the Ming Great on climb-over behaviors in mountain operations Wall may have had greater traffic capacity, with and traffic are quoted from the empirical values of slope-based classification of infantry trafficability proposed by Mauricio Nicolas Vergara (Table 5). Table 5. Cost assignment based on slope accessibility This formed the basis of reclassification of the (Vergara, Bondesan, and Ferrarese 2017). terrain used to build the cost raster in the Arc Slope classification by Revised slope GIS analysis of the cost-path, which helped us to Marinelli classification Cost value observe the terrain accessibility clearly and analyze Gentle < 10° Gentle < 10° 1 Moderate 10°–25° Moderate 10°–25° 4 the planning intentions of the facilities, including Steep 25°–45° Steep 25°–37° 16 secret gates. Cliff > 45° Very steep > 37° No value (infinite) 嘉靖 大同 延绥 宁夏 12 Z. LI ET AL. Figure 9. Terrain trafficability and cost-path analysis of Longyu Kou. 4.1. Side attack mode the range beside the valley’s main pass, posing a threat to the enemy’s flank or rear as they invaded the two General Qi Jiguang (戚继光 1528–1588 A.D.) explained ravines. the function of secret gates in the defense of the pass as follows. “A secret gate should be created below each watch- 4.2. Joint defense mode tower. It is convenient for firearm-shooting outside the wall, and enables the troops to go out to defend the The density of secret gates along the defense line wall against the enemy on the side slope”(Qi 1965). directly affects the Great Wall’s local defenses. On this The ancient rulers often used the highest points of topic, Li Shiao (李士翱 1488–1562 A.C.) stated the the mountains in front of the Great Wall to build following: “There are nine fortresses along the Great Wall in perimeter fortifications, as these locations were favor- able for long-range observation in the direction of the Hedong, Ningxia (宁夏河东 ), which stretch for more valley connected to the pass. If necessary, troops could than 200 Li (about 112 kilometers). There are four be sent to attack the invader’s flanks in the valley. As secret gates in Huamachi, Anding, Xingwu, and Figure 9 illustrates, the Longyu Kou (龙峪口 ) and the Qingshui, each 60–70 Li (about 33–39 kilometers) th 17 water gate are separated by a hill. X1, X2, and X3 apart. These face straight into the region occupied had high defense facilities (they are type-DL) and by the enemy, where the enemy is more likely to opened toward the steep hillside to ensure protection find our weakness. There is no chance of winning of the terrain. These three gates opened on the top of there for us” (Li 1962). JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 13 Figure 10. Terrain accessibility and cost-path analysis of the secret gates of the Simatai pass. The Simatai pass (司马台 ), for example, has five outside the wall are conducive to traffic connection secret gates within 500 meters on both wings (Figure between the five secret gates with a distance of only 10). According to the cost path analysis and the existing 200–300 m. The secret gates of the Simatai pass exhibit traditional mountain path, the topographical conditions clear characteristics of mutual cooperation. Figure 11. Terrain accessibility and cost-path analysis of the secret gates of Zhuanduo Kou. 14 Z. LI ET AL. Figure 12. The typical defense mode of the Ming Great Wall with secret gates as a key element. 4.3. Connecting defense lines Zhuanduo Kou (砖垛口 ), Shaling Kou (沙岭口 ), and the branch wall, which constitute the core of regional The periphery of the Great Wall line includes numerous defense. supplementary defense facilities, such as trenches, st The east side of the 21 watchtower is a weak parapets, and beacon towers. Use of these facilities point of regional defense. Therefore, a parapet would have required military personnel to shuttle fre- about 1.5 m high was erected 5–10 meters outside quently between multiple defense lines to achieve st the 21 watchtower, and neatly arranged shooting cooperation between defense fortifications. The secret holes for harquebus and cannons open onto the gates played a key role in such transportation. As parapet. Located at a distance of 50–100 m from st Figure 11 indicates, the 21 watchtower in this parapet are the ruins of another 400 m-long Jinshanling (金山岭 ) guards the fork connecting parapet composed of a cliff with rubble masonry. Figure 13. The horse market of the Ming Great Wall in ‘San Yun Chou Zu Kao 三云筹俎考 ’ (Wang 1969). JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 15 Figure 14. The secret gate in the horse market of the Ming Great Wall. Thus, the main line and parapets formed three lines frontier area gradually increased. With the intensifica - of defense. Z1 is a straight-through secret gate with tion of land annexation, the lack of farming resources wall-climbing steps (type-ZD3 in Table 1) that con- led to the collapse of the garrisoned farming system nects the two exterior defense layers. (Liao 2010). Thus, the relatively rich resources coming The variety of facility coordination indicates that in from outside the border buffered the effects of the Ming Great Wall system did not rely on a single internal social pressure. Pang Shangpeng (庞尚鹏 passive defense strategy but, rather, implemented an 1524–1580 A.D.) made the following point in his mem- active defense strategy. It comprised multiple oirs when rectifying the garrison order in Gansu district defense lines and fortress groups, with the secret (甘肃镇 ) as an imperial envoy: gate system playing a key role. Based on observa- “The military officers originally issued a ban against tions of the site selections for the secret gates along going outside the border without permission, which the whole line, the complex cooperation mode is prevented farming outside the border. Why not build summarized (Figure 12). secret gates on the trenches of the Great Wall that are close to water sources such as rivers and flood areas, and allow the nearby residents to pass through to use 5. The broader roles of secret gates in the the wasteland with soldiers guarding from the heights historical development of the frontier of the wall?”(Pang 1962). Later records of Gansu local chronicles confirmed In addition to playing an important military role in that this proposal was implemented: “ Zhenfan Chuan the Ming Great Wall’s military defense mechanisms, ( ) . . . there are 50 beacon towers along the Great the secret gate also fulfilled numerous non-military Wall, one every five Li. Each has a secret gate, allowing roles. Historical texts that document important dip- woodcutters to come in and out through.” (Zhang 1999) lomatic events, trade activities, and official policy in Consequently, the secret gate became a survival tool border areas frequently mention secret gates. Based for poor garrison troops and civilians, enabling them to on historical information mining, the secret gate’s cross the border to cut wood and cultivate crops. This specific functional performance in a non-military was key to maintaining social stability in the border areas. context will be analyzed and discussed in this section. 5.2. Border trading 5.1. Garrisoned farming and logging Secret gates were also an important facility in the border market along the Ming Great Wall, with The effective operation of the Great Wall’s defense market castles, watchtowers, barbican entrances, system was directly affected by local economies and and other facilities constituting the market defense people’s livelihoods in border areas. During the long- system (Figure 13). The narrow scale of a secret term and stable development that took place during gate allows only one person to lead a horse in and the middle and late Ming period, the population in the 镇番川 16 Z. LI ET AL. out. This is conducive to controlling the flow of Thirty years after Altan-Khan’s death, however, people and preventing chaos, market grabbing, Prince Su-nang (素囊台吉 ) stopped paying tribute to and other harmful behaviors. The Ming Dynasty the Ming Dynasty as a result of dissatisfaction with the and Mongolian tribes also established detailed Dynasty’s recognition of Bushitu’s (卜石兔台吉 ) suc- mutual market rules:“If the Mongols do not enter cession to the throne of Khan. Wang Shiqi (王士琦 ), through the secret gate but secretly climb over the vice governor of Shanxi Province, once recorded the wall, when caught, 19 cattle and sheep will be process of coping with the border crisis: “I wrote a confiscated as punishment”(Wang 1969, 247);“Any letter to the general, asking the castles along the officer who dares to sell harnesses through secret Great Wall to rectify their troops and weapons, repair gates will be immediately punished for collaborat- beacon towers and warning facilities, patrol and guard ing with the enemy”;“Let the interpreter go to the day and night, and threatened to block the secret Mongols and announce that it is not allowed to gates in person on January 15 (in the lunar calendar). take in count the horses that are dying and cannot Prince Su-nang and his twelve tribes panicked and all be ridden. Those horses with tongue broken, mane came to ask for tribute. On March 2, I personally went cut, throat stabbed, stomach poured into by sand, to the market to receive tribute . . . ” (Wang 1969, 243) and those who are too young to be fed forage are Nomadic tribes are highly autonomous and geogra- not allowed to enter the secret gate” (Wang 1969, phically dispersed, and their economy largely depends 259). Thus, secret gates were widely used in the on trade, plunder, and other auxiliary economic markets along the Ming Great Wall as core chan- sources of non-nomadic production (Wang 2008). nels in specific transaction processes. Figure 14 Thus, by closing secret gates and banning folk trade, illustrates the known location of the secret gate Mongolian tribal nobles could often be compelled to in the horse market site. compromise politically. With the help of widely distrib- uted geographical channels, such as secret gates, the Ming government could respond flexibly to the 5.3. Political contacts demands of different nomadic groups and avoid the The Great Wall was the product of political decision- systematic impact of local disputes on the border making. Therefore, the study of the Great Wall site may situation. constitute a type of foreign policy archaeology (Waldron 1990). It was also the lever and stabilizer of official political and economic relationships marked by 5.4. Relativity of the appellation “secret gate” the “tributary system and border trade” (Li 2017). The above historical roles demonstrate that the Secret gates played an irreplaceable role in the secret gate was known by those on both sides of “micro-circulation” of material and information the Great Wall in the context of their long commu- between the two sides of the border areas and were nication and interaction. Therefore, the secret gate’s likely to be important points of communication. One nomenclature seems to be inconsistent with the historical text states: reality, but throughout the Ming Dynasty, the title “Tuotuo (the son of Altan-Khan) led about ten riders did not change among the government or the peo- to the secret gate of Ningyuan castle in Xuanfu town. He ple. Today, numerous villages or places named “an- called out to the translator and swore by his sword for men-dun” (暗门墩 meaning “the beacon tower with peaceful trade with the Ming Dynasty.”(Ming Shi Zong a secret gate”) and “an-men-cun” (暗门村 means Shi Lu 1983) “the village next to the secret gate”) still exist After establishing stable political relations with Altan- throughout the Ming Great Wall area. On this Khan ( 1507-1582 A.D.), the Ming government issue, we may derive inspiration from the ancients’ even tacitly allowed his tribe to cross the Wall defense understanding of the secret gates of the Ming Great area in Hexi ( ) through the secret gate and Wall. Lu Xiangsheng (卢象升 1600–1639 A.D.) once travel between Qinghai( ) and the northern grass- suggested to the emperor that he unseal the secret land: “The tribal leaders who enter through the gates along the border to allow soldiers and civi- Shuiquan secret gate and ShiXiakou secret gate follow lians to go out to cut wood so as to improve the above two routes respectively. The commander of people’s livelihoods and open up the information the defense zone should lead the army to escort them channel from the north: “The wall blocking and port out from Biandu Kou ( ) within a time limit, and closing are just covering our eyes and ears our- the tolerance for their staying is forbidden. The tribes selves. According to the system handed down by returning from Qinghai should also be escorted and our ancestors, there are many secret gates under monitored . . . .” (Ming Shen Zong Shi Lu 1983) the border wall, just as people have holes in their According to search results for ‘暗门 ’ as a keyword in the National Database for Geographical Names of China (available at https://dmfw.mca.gov.cn/). 扁都口 青海 河西走廊 俺答汗 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEERING 17 bodies. People do not totally close their features to port system, provides new perspectives for stop harmful things entering the body . . . ” (Lu further discussion regarding the closed or open 1829). In Lu’s discussion on the secret gate, we nature of the Ming Great Wall. find the plain and dialectical philosophy of Chinese thought traditions: the meaning of “secret” As is typical of historical cultural routes, the Great (暗 ) also goes beyond the narrow concept of con- Wall includes many tangible elements with cultural cealment in a material sense and becomes a relative significance that have emerged from multi-dimen- concept with broader denotative significance. sional exchanges between different groups It should be noted that the secret gate was a formal throughout the Great Wall area. The relatively scat- port and the resulting folk or official exchanges were tered heritage elements illustrate the interaction of under the direct management of the Ming govern- movement along the route (World Heritage Centre ment, as reflected in the above research. Therefore, 2019). Secret gates or other facilities were important the “secrecy” of the secret gate is not necessarily material vehicles for multi-dimensional interaction non-governmental, local, or temporary. Its opening and movement and are now a key element for and closing often reflects changes in the official policy augmenting knowledge of the roles of seemingly toward the nomadic tribes in the north. The “secrecy” isolated defense facilities in the overall system. of the secret gate is often reflected in the limited From a holistic perspective, the characteristic statis- impact of local interaction and the flexibility of policy tics and comparative observations of various facil- practice, which supplemented the overall border ities synthesize the macro- and micro-historical defense policy. perspectives, lending greater depth to research into the Great Wall. The establishment and application of the three- 6. Conclusion and discussion dimensional image database of the Ming Great Wall has overcome the constraints of the vast spatial scale The secret gate’s function has been observed and and considerable geographical segmentation of the analyzed by considering the architectural scale, the remains, improved the efficiency of heritage informa- regional scale, and the broader historical narrative tion processing and the accuracy of site observation, background; the conclusions may be summarized and accelerated heritage exploration and the formula- from three aspects: the form of historical buildings, tion of scientific protection strategies. the planning purposes and defense mechanisms, and the historical role and influence Disclosure statement (1) The secret gates of the Ming Great Wall consti- No potential conflict of interest was reported by the author(s). tute a relatively independent hierarchy of pass systems, with the widest distribution in the Great Wall passageways. To cope with different Funding terrain conditions, military purposes, and traffic demands, various architectural types with differ - This work was supported by the National Natural Science ent functional characteristics were developed, Foundation of China [51878437,51878439,51908179]; the Social Science Foundation of Hebei Province of China which can be classified according to their func- [HB19YS036]; Project of Key Laboratory of Ministry of tional dimensions. Culture and Tourism ; the youth foundation for (2) The various cooperation modes of secret gates humanity and social sciences of the Ministry of Education with other facilities reveal that the defense [17YJCZH095]. mechanisms of the Ming Great Wall included a strong active defense, launched outside the wall, such as flank attack and containment Notes on contributors behind enemy lines, which is in contrast to the Zhe Li is the associate professor who teaches architectural stereotypical view that the border defense design and history in the School of Architecture of Tianjin depended simply on conservative linear University. He focused on landscape archaeological research fortifications. of ancient military architectural heritage and related heritage protection. At the same time, he has long been engaged in (3) Secret gates were an important material media- the research on the spatial quantitative analysis method of tor of the Ming government’s official political traditional settlements based on UAV low altitude photo- and economic relations with Mongolian tribes, grammetry data. which reflects the flexibility of the Ming Xiaolong Tuo is a doctoral student majoring in architecture in Dynasty’s frontier policy in practice. Therefore, the School of Architecture of Tianjin University. He has been the discovery of secret gates, which form a basic devoted to the study of the history of ancient Chinese 18 Z. LI ET AL. military architecture with the current research focuses on the Ha, Z. 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Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: Mar 4, 2023
Keywords: Secret gate; the Ming Great Wall; photogrammetry; image database; defense mechanism
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