Considering the Defenses of Kibe Castle (Katano Castle) from Aerial Photographs (3)
──The Full Picture of a "Muddy Stronghold" Revealed by 1948 US Military Photographs and Hydraulic/Topographic Analysis
Location: Kibe, Katano City, Osaka Prefecture
Type: Group-enclosure flatland castle
Other Names: Katano Castle
Remains: Kirigishi (steep cliffs), moats
Castellan: The Anmi clan (Anmi Ukon)
Designation: 2017 Katano City Designated Historic Site
Introduction: "Lost Remains" Captured in 1948 US Military Aerial Photographs and the Re-evaluation of Kibe Castle
Most flatland castles (hirajiro) of the Sengoku period in the Osaka Plain have disappeared from the surface due to urbanization and residential development since the period of high economic growth. Famous flatland castles such as Wakae Castle, which served as the shugo-sho (provincial constable's office) of Kawachi Province, and Ibaraki Castle in Settsu Province have also been buried underground, making it difficult to visually identify their original layouts from the surface. Amidst this, Kibe Castle (referred to as "Katano Castle" in literature), located in the center of Katano City, remains as a rare site that preserves earthworks and moat traces such as the kirigishi of the main and second enclosures, and the Honmaru Pond on the surface.
However, the current Kibe Castle site has also been altered by postwar development and land readjustment, and there are aspects where the full scope of the Sengoku period defense network cannot be grasped solely from the remains visible on the surface. A clue to this is the aerial photograph taken by the US military (USA) on March 19, 1948 (Showa 23), provided by the Geospatial Information Authority of Japan. When examining these aerial photographs closely, the heights of earthworks that have disappeared due to current residential development, minute depressions, traces of waterways, and even underground geological structures remaining as differences in vegetation (vegetation marks) emerge clearly.
Following the previous discussion, this content focuses on the 1948 US military aerial photographs. Incorporating the results of excavations by the Katano City Board of Education and professional insights from the Cultural Tourism Division of the Katano City Regional Promotion Department, we present three important hypotheses regarding Kibe Castle's defense system—"The northern mud-field barrier line from the Menjo River," "The reality of the southern outer defense line (A-H)," and "The parallel earthworks along the southern dissected valley (Point I)"—to consider the defensive structure of Kibe Castle, which was called impregnable despite being a flatland castle.
Chapter 1: The Northern and Western Barrier Line via Menjo River Water Diversion: Verification of Hydraulic Characteristics and "Arbitrary Mud-Field Creation"
1. Hydraulic Characteristics of the Dodo River and Menjo River and Professional Views
When considering the northern defense of Kibe Castle, the existence of a group of waterways flowing east-west to the north of the castle area is essential. There was a theory that the "Dodo River" flowing north of the castle was an outer moat, but careful verification was required from a hydraulic perspective and the micro-topography of the site. In this regard, the view of the Cultural Tourism Division of the Katano City Regional Promotion Department contains important suggestions for elucidating the hydraulic reality.
According to their point, the Dodo River flows at a lower elevation compared to the Menjo River flowing to the north, and the current observed flow volume is clearly less than that of the Menjo River. If one were to attempt to introduce enough water from an external source to cause the Dodo River to overflow, the question of where the water source would be arises. Furthermore, even if a large amount of water were forcibly drawn in, the increased flow would erode and destroy the unnatural, winding waterway itself, making it difficult to maintain the multi-angled channel shape.
In contrast, the "Menjo River," which flows in parallel further to the north, has been known since ancient times in folklore as a river that repeatedly broke its levees and flooded. As the origin of the river's name suggests—that the land tax of surrounding rice field owners who suffered damage from flooding was exempted—the existing meandering channel form itself vividly tells the characteristics of a natural river that repeatedly flooded. An even more important point is that the Menjo River has become a "ceiling river" (tenjogawa), where the riverbed has become higher than the surrounding flat land due to sediment accumulation.
2. The Mechanism of "Arbitrary Mud-Field Creation" and Stopping Power Against Armored Soldiers
It has been proven in early modern and modern surveys that the low-lying wetland area extending from the north to the west of Kibe Castle (the Amano River floodplain in the Nagasuna district) was land that easily became waterlogged and turned into bottomless swamps due to rainwater and other factors. This matches the description in the "Muromachi-dono Nikki," written in the early Edo period, which states, "The castle is called Takatsuno to the north, and it is a deep swamp where horses cannot stand."
When diverting water into the moat area and outer low-lying wetland area north of Kibe Castle with human intent to construct a defensive barrier line, the method of drawing water through irrigation channels from the Menjo River, which has become a ceiling river and flows at a higher elevation, is rational. While confirming the remains of the water diversion facility itself is a task for the future, "arbitrary mud-field creation" by controlling the water flow from the Menjo River was possible.
The effect of this hydraulic manipulation on defense is dramatic. Against the clayey sedimentary soil layer (silt/clay layer), even if the amount of water drawn into the moat area is only about 30 cm, the stirring of soil and water creates a quagmire that deeply traps one's footing. If a soldier wearing heavy armor and carrying several tens of kilograms of equipment enters this quagmire, they sink into the mud due to their own weight, losing mobility such as walking or jumping. Furthermore, if the water depth is maintained at about 1 meter, crossing or assault approaches become physically impossible due to the dual viscous resistance of water pressure and clayey mud.
[Structural Mechanism of the Northern Hydraulic Defense Line]
[天井川：免除川]（標高高・氾濫河川）
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├─（人為的取水・導水路）
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[北側堀部・低湿地帯]（粘土質堆積土層）
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├─ 水深30cm：過酷な泥濘化 ➔ 甲冑兵の足元を埋没・機動力喪失
└─ 水深1m ：深泥・水圧障壁 ➔ 北側強襲を阻止
│
[本郭・二郭の切岸]（傾斜40〜50度の急崖）In this way, the north side of Kibe Castle was fortified by a "water/mud composite barrier line" that fused the hydraulic potential of the natural floodplain and the ceiling river while minimizing artificial excavation.
Chapter 2: Verification of the Southern and Eastern Outer Defense Lines (A-H)
1. Detection of Vegetation Traces in 1948 Aerial Photographs
A close examination of the 1948 US military aerial photographs reveals, from the southeastern to the eastern part of the Kisabe settlement, a clearly visible band of bamboo groves and trees that is unnaturally regular and straight, distinct from the surrounding rice paddies and residential plot divisions.
From the perspective of natural science and geomorphology, constructed sturdy earthworks and elevations provide a better drainage environment (dry, slightly elevated ground) compared to the surrounding rice paddies and lowlands. It is highly likely that this geological difference was inherited as 'vegetation marks' that selectively allowed specific vegetation (bamboo groves and trees) to grow in later generations.
Based on this linear vegetation line on the aerial photograph, a hypothesis is derived that at the time, baileys A and B were continuously connected, forming a 'single massive outer perimeter earthwork' to defend the southeastern part of the main bailey. It is thought that the top of this earthwork (the upper part) was designed as a 'combat walking space (umamichi)' for soldiers to move and deploy rapidly, and to launch flanking attacks or interceptions against enemy forces approaching from the south.
2. Structural Verification of Each Point (A to H)
In response to this 'massive earthwork/umamichi hypothesis,' and based on the response from the Katano City Cultural Properties Division and data from archaeological surveys and cadastral maps, a re-examination of each point on the outer defense line from A to H revealed the reality of a complex defense line, rather than one consisting simply of earthworks.
Straight Earthwork (C) It is depicted as a 'thicket' in old Edo-period maps, and since a slight elevation is recognized in the current topography, it is safe to judge it as an earthwork terrain. However, there is a section near the middle where the elevation locally drops and the earthwork is interrupted. This suggests the possibility that it was not merely a trace of destruction, but that a castle gate or entrance (koguchi structure) was provided here.
Point D The western half corresponds to a pond/marsh that existed around Kotsuji Temple, and the eastern half covers the Kotsuji Temple cemetery (high ground). Rather than an independent earthwork, this is evaluated as a corner of the Kotsuji Temple bailey terrain (a complex of water moats and high ground) that was incorporated as a southeastern outer bailey of Kisabe Castle.
Point E Recorded as a 'field' in the Meiji-era cadastral map, the current situation is a narrow path slightly recessed from the surrounding rice paddies and residential land. While it has been estimated as an earthwork/bailey-like terrain in the layout maps produced by Takahiro Umabe and others, given the concave tendency of the current terrain, it is appropriate to view it as traces of a moat, passage, or depression defense line accompanying an earthwork.
Point F Based on the Meiji-era cadastral map and the depression in the current terrain, this is a point where a 'pond' once existed. It is highly likely to be traces of a 'moat (dry or water moat)' that delineated the outer perimeter, rather than an earthwork.
Point G This is a point where a waterway currently runs. What is noteworthy is the high-elevation 'pentagonal or hexagonal plot' located to the north of Point G. This polygonal plot, which is also depicted in the layout maps by Hitoshi Nakai and others, is presumed to have functioned as a powerful 'outer bailey/gate stronghold' to defend the northeastern entrance (approach from the Yamane Kaido/Kuraji direction) of Kisabe-go (Kisabe Castle).
A-B - Continuous tree band on the southeast side of the main bailey - high ground on the edge of the terrace - fundamental earthwork/elevation directly defending the southeast part of the main bailey
C - Line of bamboo groves/thickets extending in a straight line - 'thicket' in Edo maps, elevation and central interruption in current terrain - Straight Earthwork. The central interruption is a possible site of a gate/koguchi.
D - Dark shadows indicating moisture and elevation, Kotsuji Temple pond/marsh (west) and cemetery high ground (east) - A corner of the Kotsuji Temple bailey. - Water moat/pond complex delineating the outer bailey
E - Long, narrow band-like shadow, cadastral map shows field, current situation is a narrow path recessed from residential land - Complex of earthwork/moat traces. A depression forming a turning point in the layout
F - Clear depression/pond-like shadow, record of a pond in the Meiji cadastral map, depression on the ground surface - Traces of a moat. Traces of a water moat or dry moat delineating the outer perimeter
G-Row of trees along the waterway and the northern elevation; current waterway, high-elevation pentagonal/hexagonal plot to the north-Northeast gate approach base. Controlling the street entrance with a polygonal enclosure
H-Line at the eastern end of the settlement, the eastern end of the terrace, and the slope transition line toward 'Aza Ichiba'-Eastern outer enclosure terminus. Blocking line against intrusion from the direction of the Yamane Kaido road
Through the above detailed examination, it is proven that the line from A to H was not covered by a single massive earthwork alone, but was an 'outer composite defense line' that continuously combined earthworks (C), gate sites, temple enclosures (D), moat sites (F), waterways, and polygonal enclosures (G).
Chapter 3: Defense Line Along the Dissected Valley: The 'Valley-Parallel Earthwork' Hypothesis at Point I and Wide-Area Defense
1. Geomorphological Analysis of Point I (Mounded Terrain Along the Southern Dissected Valley)
Expanding the view of the 1948 aerial photograph further south (around Katano City Hall and the former Katano Elementary School), an independent mounded elevation (Point I) can be confirmed along the northern edge of the large southern dissected valley (2–7m deep, 50–80m wide).
This Point I is positioned parallel to the dissected valley (an area that was once a vast expanse of rice paddies and muddy fields) running east-west at the southern end of the Kisabe settlement. I propose the hypothesis that this Point I is the trace of a 'valley-parallel earthwork' built on the north bank of the dissected valley, which served as a natural, massive outer moat (a muddy field zone approximately 80m wide and 500m long).
[Conceptual diagram of the wide-area north-south cross-section of the south side of Kisabe Castle (around Point I)]
［南側：山根街道・私市道方面］
│
▼
［天然の外堀：南開析谷］（幅50〜80m、泥田・湿地帯、T.P.+20.5m）
│
▼
［I地点：谷並行土塁］（天然の崖線＋人工土塁による遮蔽・射撃陣地）
│
▼
［南側平坦面 / 空堀ライン］（T.P.+24.0〜25.4m、クランク状堀）
│
▼
［本郭・二郭・三郭・出郭（光通寺）］（主郭部高台、T.P.+26.0〜27.8m）
2. Military Role of Point I in Wide-Area Defense
The south side of Kisabe Castle is a transportation hub where the 'Kaigake-do (Hoji-goe)' and 'Ifune Kaido' roads leading to Yamato Province, as well as the 'Yamane Kaido' connecting Hirakata and Hoshida, converge. If enemy forces from the south were to approach Kisabe Castle, they would have to pass through the southern dissected valley.
The earthwork at Point I functioned as a defensive position for adding horizontal and overhead fire with bows and arrows or firearms (the large 'O-teppo' guns and the Yasumi-style gunnery that the Yasumi clan boasted of) against enemy troops stalled in the muddy fields of the dissected valley. By combining the natural terrain gap (dissected valley) and the artificial earthwork (Point I), it is presumed to have served as a frontline blocking screen against assaults from the south.
Chapter 4: Multilayered Defense Network and the Pioneering Nature on the Eve of the Oda-Toyotomi Period
1. Multilayered Defense System Fusing Hydraulics, Earthworks, and Natural Terrain
Synthesizing the reading of the 1948 aerial photograph and the results of archaeological excavations, the defensive structure of Kisabe Castle is reconstructed as a multilayered defense network that transcends the mere framework of a residence.
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Outermost enclosure (natural barrier + water diversion line)
North side: Water-logging and muddy field blocking line via water diversion from the Menjo River.
West side: Amano River floodplain (muddy field zone) in the Nagasuna district.
South side: Rice paddy and wetland zone of the dissected valley spanning 50–80m in width (the outer moat of the 'Muromachi-dono Nikki').
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Outer defense line (artificial structures + auxiliary enclosures)
South to East side: Composite defense line of the straight earthwork from A to H, gate sites, Kotsu-ji Temple (auxiliary enclosure), Point F moat site, and Point G polygonal enclosure.
Along the southern dissected valley: Interception position via the valley-parallel earthwork at Point I.
West side: Control of the Kisabe Kaido road via the enclosure near the post office (high ground sandwiched between east-west dry moats).
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Inner Enclosure Group (Central Layout)
A linked enclosure layout consisting of the Main Enclosure, Second Enclosure, Third Enclosure, and Fourth Enclosure.
Sharp steep slopes (kirigishi) created by cutting and filling the ground layers (40–50 degree incline, 3–5m relative height).
Subdivision via box moats and V-shaped moats (water moats, dry moats, and stepped structures).
【Bird's-eye view image of Kisabe Castle's overall defensive structure】
[北] 免除川（天井川） ──（導水）──> 帯水泥田帯 ＋ 百々川（箱堀）
│
[西] 天野川氾濫原 ── 郵便局付近郭 ──> 【本郭・二郭・三郭・四郭】 <── G地点多角形郭・山根街道 [東]
（長砂泥田） （西外堀） │（切岸・内堀・瓦葺建物）
│
A〜H外郭防衛ライン（C土塁・光通寺出郭・F堀跡）
│
[南] 山根街道・私市道 ──（南開析谷泥田）──> I地点谷並行土塁 ＋ クランク状南堀2. Advanced evaluation in castle history indicated by the use of roof tiles
Another essential element in discussing the defenses of Kisabe Castle is the presence of a large quantity of roof tiles unearthed from the Main Enclosure, Second Enclosure, and Outer Enclosure (Kotsuji Temple) during archaeological excavations.
Stylistic analysis of the excavated eaves-end tiles and eaves-round tiles (jaw-attachment technique, early inner-beating technique, and trefoil arabesque patterns) has confirmed that these tiles were produced in the mid-to-late 16th century (Eiroku to Genki eras, circa 1558–1573). This is an advanced example that predates the creation of tile-roofed castles by Oda Nobunaga at Azuchi Castle (built in 1576).
The lord of Kisabe Castle, Yasumi Ukon (and Yasumi Munehusa), was not merely a local landowner but a powerful warlord who confronted and negotiated with the hegemonic powers of the Kinai region, such as Miyoshi Nagayoshi, Matsunaga Hisahide, and Oda Nobunaga. The fact that they incorporated the tile-laying techniques of nearby influential temples (such as Kotsuji) and the tiles themselves into the castle, and constructed tile-roofed buildings (turrets and gates) at key points in the Main and Second Enclosures, proves that they were attempting to evolve into a "showcase castle" that demonstrated political authority to the surroundings, in addition to strengthening military fire prevention and fire resistance.
Conclusion: Kisabe Castle as a "Three-Dimensional Military Science City" that overcame the weaknesses of a flatland castle
The defensive structure of Kisabe Castle emerged through the analysis of 1948 US military aerial photographs and the collation of data on topographical changes since the modern era.
Although Kisabe Castle appears at first glance to be a "flatland castle" with little relief, it was a "three-dimensional military science castle" that integrated the following systems at a high level.
Free control of hydraulic barriers By maintaining a water diversion system from the Menjo River, which is a suspended river, and intentionally turning the low-lying areas on the north and west sides into deep mud, they blocked the approach of heavy infantry.
Multi-stage interception via multi-layered outer lines By arranging the outermost southern dissected valley (muddy field) and the I-point earthwork, as well as the outer composite lines leading from A to H (straight earthworks, gates, Kotsuji outer enclosure, and polygonal enclosures), they controlled the enemy's invasion routes (highways) like a spider's web.
Central defense via steep slopes, inner moats, and tile-roofed structures The central enclosure group (Main, Second, and Third Enclosures) created high relative heights and steep slopes through extensive cutting and filling, forming a solid central position equipped with advanced tile-roofed buildings.
In the 3rd year of Genki (1572), when Matsunaga Hisahide built siege castles in the surrounding area to capture Kisabe Castle, Oda Nobunaga himself sent reinforcements and deployed senior vassals (such as Sakuma Nobumori, Shibata Katsuie, Niwa Nagahide, and Akechi Mitsuhide) to firmly surround the siege castles with a "shishigaki" (large-scale siege network). This fact tells us that Kisabe Castle was not just a simple flatland castle, but a strategic stronghold that swayed the hegemony of the Kinai region.
The green lines and shadows of muddy ground etched into the 1948 aerial photographs are the crystallization of the tenacity and advanced castle-building technology of the Yasumi clan and the surrounding Sengoku warlords who tried to overcome the weaknesses of flatland castles on the front lines of the Sengoku turmoil.
This content was created based on Gemini through repeated dialogue with the contributor.
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