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The Remnants of Structures Thought to be Seirō in the Historical Site of Noshima Castle

Yoshimi YAMAGUCHI*1

The remnants of six sōbashira-style earthfast pillar structures were found in Noshima Castle. They consist of square 2 ken × 2 ken bases and, as such, are likely to have been seirō. The archeological survey report does not clearly indicate the role of these structures; the report argues that they may have been seirō, but it also expresses doubt by questioning what useful role such structures could have served and why there were so many of them. In this article, I reaffirmed that the remnants of sōbashira-style earthfast pillar structures discovered in Noshima Castle were all seirō. Having examined these seirō as well as the seirō in other medieval fortresses, I concluded that they were erected to keep a close lookout over the sheer drop on the outside of the fortress over the dobei. Also, have been erected from the middle to late 16th century, they belonged exclusively to a period of conflict in Japan’s history, marked by fierce battles between large armies.

KEYWORDS: Earthfast pillar (Hottate-bashira), Sōbashira-style, Dobei, Yamajiro, Umijiro

１．Introduction seirō (井楼：watchtowers), tall structures for observing far- off distances. However, it would be peculiar for a fortress The site of the island fortress of Noshima (能島：a as small as Noshima Castle to have had as many as six seirō. national historic site of Japan in Miyakubo-cho, Imabari The archeological survey report1) does not offer a City, Ehime Prefecture, hereinafter referred to as “Noshima definite indication of the role of these structures. On the one Castle〔能島城〕”) comprises a medieval yamajiro (山城： hand, it puts forth the possibility that they may indeed have hilltop fortress), or umijiro (海城：sea fortress), that served been seirō, but on the other hand, it questions whether such as the headquarters of the Noshima Murakami (能島村上) tall lookout structures would really have been necessary clan, who were renowned as pirates and privateers. In 2001, given that the fortress’s existing enclosures already offered a project to preserve and restore Noshima Castle began, excellent vantage, and whether there would have been a leading to a fully-fledged archeological survey of the site need to install as many as six of them on the north side of Note 1). the island. The archeological survey team discovered the In this article, I reaffirm that the earthfast pillar remnants of six sōbashira-style ( 総柱) earthfast pillar structures with 2 ken × 2 ken bases that were discovered in (hottate-bashira〔掘立柱〕) structures with a square 2 ken Noshima Castle did indeed serve as seirō. I also examine (間) × 2 ken base (ken being a unit of number between pillar similar remnants found in other medieval fortresses or holes). Many of the pillar holes were large and deep, with a castles (chūsei-jōkaku〔中世城郭〕) in Japan. I then offer diameter of 40-50 cm and a depth of 40-50 cm. These are a fresh opinion, namely, that during the middle and late 16th sōbashira-style Note 2) earthfast pillar structures, which have century—when upheaval and military conflict throughout a square 2 ken × 2 ken base and pillar holes that are large the country was particularly intense—seirō were not used and deep; this generally suggests that the structures were for observing far-off distances, but to watch for

 *1 Hiroshima University 平成29年12月22日受理

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approaching enemies. honmaru (本丸：main bailey; Fortification I) was constructed at the uppermost kuruwa-enclosure, a ni-no- ２．Outline of Noshima Castle maru (二之丸：second bailey; Fortification II) around the honmaru, and a san-no-maru (三之丸：third bailey; Noshima Castle was a medieval umijiro located in Fortification III) on the kuruwa-terrace below the western the Geiyo Islands (芸予諸島) in the Seto Inland Sea (瀬戸 side of the ni-no-maru. Additionally, at the end of the ridge 内海). The fortress covered the Noshima and Taisakijima leading the south from the ni-no-maru, there was a tōnan- (鯛崎島) islands. Being situated on a strait between the demaru (東南出丸：outer bailey; Fortification IV), and at islands of Ushima ( 鵜島) and Ōshima ( 大島) called the end of the ridge leading east from it, a yabitsu (矢櫃： “Miyakuboseto ( 宮窪瀬戸),” Noshima Castle was arrow-store; Fortification V). The sixth fortification was on surrounded by rapid tidal currents and small in size; its the southerly Taisakijima island; this fortification was the circumference was around 720 m, that of Taisakijima taisaki-demaru (鯛崎出丸; Fortification VI), made by around 256 m, for a combined circumference around 1 km terracing the crest of the island, as with Noshima island’s (17,829 m²). honmaru. On the northern shoreline of Noshima island, Noshima Castle was supposedly constructed by the there was a basin that served as a mooring facility second chief of the Noshima Murakami clan, Murakami (funadamari 〔船だまり〕), and on the south-western hem, Yamashiro-no-kami Masahusa (村上山城守雅房) in 1419. a plain. Because Noshima Castle was a natural fortress, During the Tenbun (天文) era (1532-1555), a conflict over there were no artificial moats or equivalent structures. the clan’s inheritance flared up between the Yoshimasu (義 益) family, the main clan line, and the Takeyoshi (武吉) family, the branch clan line. In 1546, Takeyoshi became the fifth clan chief after seizing Noshima and Mitoshima (水途 島), which had served as Yoshimasu’s headquarters. The Noshima Murakami clan had served the Ōuchi (大内) and Mōri (毛利) clans for many years, but in 1571, Takeyoshi turned his back on Mōri and pledged his allegiance to the Ōtomo (大友) clan. As a result, Noshima Castle was besieged by the Kobayakawa (小早川) clan’s guards and the forces of Innoshima Murakami ( 因島村上) and Kurushima Murakami (来島村上). After the siege, the Noshima Murakami clan returned to their allegiance to the Mōri clan and served them well in the Battle of Kizugawaguchi (木津川口の戦い) in 1576. Takakage Kobayakawa (小早川隆景) then laid siege to Noshima Castle, because Noshima Murakami did not support Hideyoshi Toyotomi’s (豊臣秀吉) campaign to subjugate Shikoku (四国征伐) in 1585. Thus, Noshima Castle saw much conflict during the middle and late 16th century. After Takakage Kobayakawa was transferred to Chikuzen (筑前) in 1587, the Noshima Murakami clan withdrew from Noshima Castle, and the fortress was abandoned Note 3). In the building of Noshima Castle, the whole of the Figure１ The Seirō-remnant of Noshima Castle two islands (Noshima and Taisakijima) were turned into a Note：■=Seirō-remnant fortress (Figure 1). On Noshima island, terraced enclosures Source：Partial modification of an image in Imabari City Board (kuruwa〔曲輪，郭〕; hereunder, kuruwa-enclosures) at of Education (2014) 1) three different elevations were carved into the hilltops. A

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The Remnants of Structures Thought to be Seirō in the Historical Site of Noshima Castle（YAMAGUCHI） 91

The archeological survey work around the kuruwa- situated on the terrace immediately below the honmaru. enclosures has uncovered the remnants of stone foundation Consisting of a largely square 2 ken × 2 ken base (1 structures, earthfast pillar structures, and many pillar holes, ken ranging from 2 to 2.2 m), this is the remnant of a while work around the shoreline has revealed that pits were sōbashira-style earthfast pillar structure (Figure 2). The bored into the reef. A large number of relics, like haji-style holes for the earthfast pillars are circular (some are (土師質) pottery and ceramicware, were also excavated. elliptical) and large, with the diameter ranging from 40 to 60 cm and the depth ranging from 30 to 55 cm. According ３．Seirō-Remnants in Noshima Castle to the archeological survey report, white porcelain dishes and other relics excavated from the holes indicate that the The remnants of six sōbashira-style earthfast pillar structure was in use from the late 15th to early 16th century. structures were found in Noshima Castle. They consist of Also, on the seirō’s western flank (approximately 2 square 2 ken × 2 ken bases and, as such, are likely to have m west of the southwestern corner), there are seven pillar been seirō. Hereunder, I outline these structures. holes arranged along the circumference of the kuruwa- The archeological survey report does not clearly enclosure. These holes might be the remains of a wall or indicate the role of these structures; the report argues that fence, but given that they are situated outside the they may have been seirō, but it also expresses doubt by fortification, it is more likely that they were part of an questioning what useful role such structures could have earthen rampart (dobei〔土塀〕). The distance between served and why there were so many of them. To simplify these pillar holes is irregular, but around 1.5 m in most cases. matters, I use the term seirō-remnant to describe the The earthfast pillar holes are circular, with the diameter remnants of an earthfast pillar structure with a 2 ken × 2 ken ranging from 40 to 50 cm and the depth ranging from 30 to base. 40 cm.

３．１ Outline of Each Seirō The Ni-no-Maru Seirō-Remnant The ni-no-maru seirō-remnant3) is situated on the The Honmaru Seirō-Remnant northeastern edge of the kuruwa-enclosure by a steep path The honmaru seirō-remnant2) is situated a little leading down to the yabitsu below. north of the center of the kuruwa-enclosure next to a steep Consisting of a largely square 2 ken × 2 ken base (1 slope (a sheer drop) leading down to the ni-no-maru ken ranging from 1.9 to 2.3 m), this is the remnant of a

Figure２ The Seirō-Remnant in Honmaru Figure３ The Seirō-Remnant in Ni-no-Maru (Fortification I) of Noshima Castle (Fortification Ⅱ) of Noshima Castle ： 2) Source Imabari City Board of Education (2011) Source：Imabari City Board of Education (2013) 3)

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sōbashira-style earthfast pillar structure (Figure 3). The The Yabitsu Seirō-Remnant holes for the earthfast pillars are circular (some are The yabitsu seirō-remnant2) 3) is situated slightly elliptical) and vary in size; the diameter ranges from 28 to west of the center of the kuruwa-enclosure. This enclosure 56 cm and the depth ranges from 20 to 52 cm (estimated). consists of a narrow terrace with sheer drops on the north No dateable relics were found here, so it is uncertain when and south sides. Although the complete set of pillar holes the structure was built. has not yet been confirmed, it is a square 2 ken × 2 ken remnant and the distance between pillar holes is The Two San-no-Maru Seirō-Remnants approximately 2 m, which indicates that this is the remnant The survey team discovered two bases that were of a seirō. probably remnants of seirō4) on the ridge jutting out northward from the san-no-maru. There are sheer drops on The Taisaki-Demaru Seirō-Remnant the east and west side of the ridge. Because the method used The taisaki-demaru seirō-remnant1) is situated near here was a trench survey, the overall outline of the the sheer drop on the northern edge of the kuruwa- structures is unclear. The two seirō-remnants are close to enclosure, a little west of center. each other, with one being north of the other. In the southern Consisting of a square 2 ken × 2 ken remnant (1 ken remnant, the central axis is oriented slightly west in ranging from 1.8 to 2.1 m), this is probably the remnant of comparison to the northern site (Figure 4). a sōbashira-style earthfast pillar structure (Figure 5). These remnants are likely to be the remnants of Because the method used was a trench survey, not all the seirō, because each one is a 2 ken × 2 ken remnant, the pillars have been confirmed. The holes for the earthfast distance between holes for the earthfast pillars is pillars are circular, with the diameter ranging from 20 to 45 approximately 2 m, and the holes for the earthfast pillars are cm and the depth of 75 cm. large, with diameters of over 40 cm and depths over 40 cm. The south pillar line of the northern site is slightly askew from the north pillar line of the southern site. Given their close proximity, it seems unlikely that the two structures were erected at the same time; one was probably built after the other outlived its purpose. It is unclear which of the two was built first.

Figure５ The Seirō-Remnant in Taisaki-Demaru (Fortification Ⅵ) of Noshima Castle Source：Imabari City Board of Education (2014) 1)

３．２ Distinctive Features of the Seirō of Figure４ The Seirō-Remnant in San-no-Maru Noshima Castle (Fortification Ⅲ) of Noshima Castle Source：Partial modification of an image in Imabari City Board To summarize the above, the archeological survey 4) of Education (2012) of Noshima Castle has identified the remnants of six sōbashira-style earthfast pillar structures with 2 ken × 2 ken

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The Remnants of Structures Thought to be Seirō in the Historical Site of Noshima Castle（YAMAGUCHI） 93

remnants, which are likely to have been seirō. One each try to raid the mooring facilities or scramble up the hill and was found in the honmaru, ni-no-maru, yabitsu, and storm the fortress. taisaki-demaru, and two were found in the san-no-maru. Regarding the building date, the only certain thing All of these seirō-remnants are situated next to a sheer drop is that the honmaru seirō was used beginning in the late on the north side of their respective kuruwa-enclosure. 15th or early 16th century. However, given that they were Notably, no such remnants were detected in the tōnan- all similarly situated and had roughly the same size pillar demaru on the southern corner of the island. holes, the six seirō were probably not erected far apart in In all six seirō-remnants, 1 ken-distance is around 2 time. There are no signs of any of the seirō being rebuilt, mNote 4). The scale of each seirō-remnant is equivalent to that the exception being the seirō-bases in the san-no-maru. of other fortresses. As for the earthfast pillar holes, while Earthfast pillar structures of this size would probably have there is some variation, many range between 40 and 50 cm endured for around 10 years, suggesting that they stood for in diameter and 40 to 50 cm in depth. To relate these seirō- only a brief period. As for the two seirō in the san-no-maru, remnants to 2 ken × 2 ken earthfast pillar structures of the as mentioned previously, the second seirō was probably 16th century in general, such structures would generally use erected after the first had finished its years of service. To wit, wooden pillars around 10 cm in diameter, for which pillar the earliest seirō in Noshima Castle was most likely in the holes of 20 cm in diameter would be sufficient. Thus, the san-no-maru. It does not require a great leap of imagination earthfast pillar holes of Noshima Castle are at least twice as to suppose that the fortress inhabitants initially built just the large as average earthfast pillar holes from the time, and it one seirō in the san-no-maru and then built more seirō in is unlikely that the structures using such thick and long the other kuruwa-enclosures to bolster defenses. In the pillars would have been anything other than seirō. middle to late 16th century would it necessary to shore up Furthermore, while the archeological survey report the fortress, so this was probably when the seirō were added points out that the holes are a little shallower than the holes Note 8). of seirō in other fortresses, this difference in depth may have reflected a height difference in the seirō structure. A ４．Seirō-Remnants in Medieval Fortresses general rule in archeology is that the upper part of a of Japan structure is around 10 times the height of the depth of the pillar holes Note 5). Judging from pillar holes discovered in the Archeological surveys of medieval fortresses of survey, the tallest seirō in Noshima Castle would have been Japan occasionally uncover the remnants of earthfast pillar the one in the taisaki-demaru. The seirō in the honmaru and structures that were probably seirō, as with those in that in the ni-no-maru would have been in joint second- Noshima Castle. The archeological survey report place, and the seirō in the san-no-maru would have been sometimes identifies such remnants as remnants of slightly shorter than these. The variation in pillar hole depth earthfast pillar structures and sometimes as the probable might have reflected differences in the length of the remnants of seirō. In this article, I use the term seirō- procured logs Note 6). remnant to describe the remnants of earthfast pillar A particularly noteworthy characteristic of the structures with 2 ken × 2 ken bases whose pillar holes are seirō-remnants in Noshima Castle is that there are as many larger than those commonly prepared for earthfast pillars. as six of them. This is peculiar because fortresses usually Such seirō-remnants have been excavated in a only had no more than one Note 7) and because Noshima number of medieval fortresses or castles of Japan, including Castle was a relatively small fortress. The large number of the sites of Kagomori Castle ( 河後森城跡) and seirō might have stemmed from the fortress being an Ogurayama Castle ( 小倉山城跡), both nationally umijiro—a fortress surrounded by the sea. Key evidence for designated historic sites, and the site of Takane Castle (高 this assumption is the fact that the seirō were erected next 根城跡), a municipally designated historic site. Hereunder, to sheer drops on the north side, offering a commanding I outline these sites with reference to the archeological view of mooring facilities, the funadamari. In other words, survey report. It should be noted that no seirō-remnants they were apparently erected in these locations to allow the have been excavated in early-modern fortresses or castles. inhabitants to keep a lookout for enemy forces who might

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４．１ Outline of Seirō-Remnants in Medieval wide and deep. SB2 is a largely square 2 ken × 2 ken base Fortresses (Figure 7). It too is the remnant of an earthfast pillar structure. The pillar holes are slightly smaller in diameter The Seirō-Remnants in Kagomori Castle than those of SB1, but they are similarly deep. The survey Kagomori Castle (Matsuno-cho, Ehime Prefecture) team found pillar holes in the honguruwa that were part of was a medieval hilltop fortress at an elevation of 172 m the dobei. above sea level and a relative elevation of 88 m. It is unclear when the fortress was constructed, but it would have been some time in the middle to late 16th century. The fortress was probably abandoned after the enactment of the Ikkoku ichijō rei (一国一城令：Law of one castle or fortress per province). The fortifications of Kagomori Castle were arranged along a horseshoe-shaped ridge. The honguruwa (本郭：main fortification) was built at the crest of the mountain, the center of the horseshoe’s curve, and the other fortifications splayed out to the east and west. At the end of the line of fortifications running to the east of the honguruwa, there was a fortification called the kojō (古城： Figure７ old fort). To the south of the kojō was another fortification The Seirō-Remnant (SB2) in Honguruwa called the shinjō (新城：new fort). Kagomori Castle has of Kagomori Castle ： 5) remnants of four earthfast pillar structures that were Source Matsuno-cho Board of Education (2008) probably seirō Note 9). Hereunder, I describe the two seirō- remnants in the honguruwa and the one seirō-remnant in The shinjō’s seirō-remnant6) is situated on the the shinjō. eastern part of the kuruwa-enclosure (Figure 8). It is a There are two seirō-remnants in the honguruwa 5): largely square 2 ken × 2 ken base (1 ken being SB1 and SB2. Of these, SB1 is situated on the northern approximately 2 m). This is the remnant of a sōbashira- edge of the kuruwa-enclosure next to a sheer drop (Figure style earthfast pillar structure. The holes for the earthfast 6). SB2 was discovered around 4 m west of SB1. SB1 is a pillars present a circular or elliptical shape. They are deeper slightly rectangular 2 ken × 2 ken base. It is the remnant of than the pillar holes in the vicinity. The central pillar hole is an earthfast pillar structure. Many of the pillar holes are

Figure８ Distribution of Structures in the Shinjō Figure６ The Seirō-Remnant (SB1) in Honguruwa of Kagomori Castle of Kagomori Castle Source：Partial modification of an image in Matsuno-cho Source：Matsuno-cho Board of Education (2008) 5) Board of Education (1999) 6)

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The Remnants of Structures Thought to be Seirō in the Historical Site of Noshima Castle（YAMAGUCHI） 95

offset slightly to the south. When surveying the shinjō, the rectangular 2 ken × 2 ken base (1 ken ranging from 1.8 to survey team also found pillar holes for the dobei around the 2.4 m; Figure 9). This was another earthfast pillar structure. circumference of the kuruwa-enclosure Note 10). The holes for the earthfast pillars present a circular or semi- elliptical shape. Many of the pillar holes are very large, with The Seirō-Remnant in Ogurayama Castle diameters of 50 to 85 cm and depths of 55 to 75 cm. The Ogurayama Castle (Kitahiroshima-cho, Yamagata hole in the western corner is smaller, the diameter 25 cm, District, Hiroshima Prefecture) is a medieval yamajiro but 50 cm deep. situated at 462 m above sea level, and with a relative elevation of 50 m, on the crest of Mt. Ogurayama and ridge The Seirō-Remnant in Takane Castle (Kuzugō leading away from the crest. Constructed before the middle Castle) 15th century, Ogurayama Castle served as the headquarters Takane Castle (known in the past as Kuzugō of the Kikkawa (吉川) clan until the clan abandoned it in Castle; Misakubo-cho, Hamamatsu City, Shizuoka 1545 Note 11). Prefecture) is a medieval yamajiro situated atop Mt. Ogurayama Castle comprised of three fortifications, Sankakuyama, at 420 m above sea level, with a relative each classified as a fortification group. There was a elevation of 150 m. Takane Castle was originally honmaru fortification group (本丸郭群) on the crest of the constructed in the early to middle 15th century by the mountain. To the northwest of the honmaru fortifications, Okuyama (奥山) clan. It was later significantly renovated there was a ni-no-maru fortification group (二の丸郭群), by the Takeda (武田) clan, in either 1570 or between 1571 and to the northeast, there was a san-no-maru fortification and 1575. The fortress was then abandoned in 1576. group (三の丸郭群). The uppermost of the honmaru Takane Castle consists of kuruwa-enclosures fortifications was the eponymous honmaru, and here lies carved from the hilltops. The uppermost of these was the the remnant of an earthfast pillar structure thought to have honguruwa (本曲輪：main enclosure). To the south of the been a seirō. honguruwa lay a ni-no-kuruwa (二の曲輪：second The seirō-remnant7) is situated a little southeast of enclosure), and to the south of this lay a san-no-kuruwa (三 the center of the honmaru. The remnant is a slightly の曲輪：third enclosure). The seirō-remnant8) is situated east of the center of the honguruwa. The remnant is a largely square 2 ken × 2 ken base (1 ken being approximately 1.8 m), and is an earthfast pillar structure (Figure 10). The holes for the earthfast pillars are circular and very large in size, with diameters of approximately 60 cm and depths of approximately 50 cm. However, the central hole does not lie on either the lengthwise or crosswise pillar lines. It is thought that this hole accommodated a pillar that supported the ladder used to climb up and down the structure. There now stands a replica seirō at this site, erected based on archeological findings. The honguruwa offered a commanding view of the region, but there were a couple of blindspots; the foothills running east to south and the foothills running west to south Figure９ The Seirō-Remnant of Ogurayama Castle are concealed from view. Thus, the seirō was probably Source：The Laboratory for Investigations into Medieval erected to compensate for these blindspots. Moreover, the Sites Cultural Division Lifelong Learning Department honguruwa was highly likely to have been circled by the 9) Hiroshima Prefectural Board of Education Matsuno-cho dobei . Board of Education (2002) 7)

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the motive for building seirō and the role they played. The first point to consider is their location within the yamajiro. In the case of Noshima Castle, all six seirō were in the northern parts of the two composite islands. In Kagomori Castle, the seirō in the shinjō is on the northwestern part of the shinjō. None of the seirō are in the center of their respective kuruwa-enclosures; rather, they are positioned on edges overlooking a sheer drop. Thus, they were evidently erected as a defense against raids on the fortress. Furthermore, a report has revealed that Kagomori Castle’s shinjō and the kuruwa-enclosures in Takane Castle were circled by the dobei. Similarly, in Noshima Castle, the Figure10 The Seirō-Remnant of Takane Castle archeological team discovered holes that accommodated Source：Misakubo-cho Board of Education (2002) 8) the pillars for the fence or dobei. Thus, it is evident that seirō were erected in kuruwa-enclosures circled by dobei. ４．２ Distinctive Features of the Seirō of The dobei were effective defensive facilities. Small Medieval Fortresses openings in the dobei wall called sama (狭間) gave cover defenders who could fire at enemies below with bows or Most of the seirō in these medieval fortresses were firearms. The downside was that dobei restricted the view sōbashira-style earthfast pillar structures with square 2 ken from the kuruwa-enclosure. In other words, they obstructed × 2 ken bases. In each case, 1 ken is around 2 m, and the the inhabitants from seeing what was happening on the pillar holes are wide and deep. sheer drop. Seirō were probably erected to compensate for Also, each seirō was erected not in the center of a this drawback. The peripheries of kuruwa-enclosures near kuruwa-enclosure but on the periphery of the fortress, the sheer drops would have been the ideal position for seirō, overlooking a sheer drop. Most notably, the multiple seirō for here the watchmen could peer over the dobei and watch that stood in Kagomori Castle were all also located next to for enemies climbing the hill. a sheer drop. If the structure was in good condition, the According to the archeological report, all seirō dobei has often been found together with a seirō-remnant. were erected in the middle to late 16th century, and they The seirō are thought to have been erected during ceased to be erected by the early-modern period. In other the middle to late 16th century. Since there are no signs that words, the seirō only existed at the end of the Sengoku they were repeatedly rebuilt, they were likely erected only period (戦国時代：warring-states period), a period of one time. No seirō-remnants have been discovered in early- conflict in which massive armies clashed. Being earthfast modern fortresses or castles. pillar structures, they probably would have endured for no more than around ten years; yet, there are no signs that they ５．The Motive for Building Seirō and were rebuilt over and over. This indirectly indicates that the their Role seirō were erected to be ready for the final stage of Toyotomi’s unification of Japan, for example. Toyotomi’s The prevailing view up until now is that seirō were ascension marked the beginning of the early-modern era of erected to allow a distant view of the area. However, since castle construction, accompanied by new defensive yamajiro were situated on hilltops, they would already have structures like tenshu (天守：main keep) and ishigaki (石 provided excellent vantage, and the inhabitants would have 垣：stone walls). These features rendered seirō completely been able to see far off into the distance from any of the redundant Note 12). kuruwa-enclosures. The added 5 or 8 m of height afforded by a seirō would have made little difference in terms of the outlook over the region. Thus, there is need to reevaluate

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The Remnants of Structures Thought to be Seirō in the Historical Site of Noshima Castle（YAMAGUCHI） 97

６．Conclusion Imabari City Board of Education (2012) (in Japanese) 今治市教育委員会編：史跡能島城跡（平成 22・23 年度郭Ⅲ In this article, I reaffirmed that the remnants of （第 2・3 次）調査報告書，今治市埋蔵文化財調査報告書第 sōbashira-style earthfast pillar structures with square 2 ken 112 集），今治市教育委員会（2012） × 2 ken bases discovered in Noshima Castle were all seirō. 5) Matsuno-cho Board of Education (ed.): National Historical Site As to why such a small fortress as Noshima Castle should Kagomori Castle Ruins (Survey Report for Honguruwa Zone: have as many as six seirō, the reason was probably because Matsuno-cho Cultural Heritage Survey Reports Vol.15), Matsuno- it was an umijiro—a fortress surrounded by sea. cho Board of Education (2008) (in Japanese) Having examined these seirō as well as the seirō in 松野町教育委員会編：国指定史跡河後森城跡環境整備事業 other medieval fortresses, I concluded that they were 概要報告書Ⅵ（本郭ゾーン，松野町文化財調査報告第 15 集 ）， erected to keep a close lookout over the sheer drop on the 松野町教育委員会（2008） outside of the fortress over the dobei. Also, have been 6) Matsuno-cho Board of Education (ed.): Historical Site erected from the middle to late 16th century, they belonged Kagomori Castle Ruins (Matsuno-cho Cultural Heritage Survey exclusively to a period of conflict in Japan’s history, marked Reports Vol.9), Matsuno-cho Board of Education (1999) (in by fierce battles between large armies. Japanese) In this article, I discussed the seirō with reference 松野町教育委員会編：史跡河後森城跡（現在までの調査と to a number of key examples. Looking ahead, I would like 成果，松野町文化財調査報告第 9 集），松野町教育委員会 to broaden this inquiry and examine all the other structures （1999） in Japan’s medieval fortresses that might have been seirō. 7) The Laboratory for Investigations into Medieval Sites Cultural Division Lifelong Learning Department Hiroshima Prefectural References Board of Education (ed.): An Excavation Report of Ogurayamajou Castle Site: 15-16th Century (A Bulletin of Investigations into 1) Imabari City Board of Education (ed.): Historical Site Noshima Medieval Sites Vol.3), Hiroshima Prefectural Board of Education Castle Ruins (2011-2012 Survey Report for Enclosure VI: Imabari (2002) (in Japanese) City Archeological Heritage Survey Reports Vol. 125), Imabari 広島県教育委員会事務局生涯学習部文化課中世遺跡調査 City Board of Education (2014) (in Japanese) 研究室編：小倉山城跡発掘調査報告書（中世遺跡調査研究 今治市教育委員会編：能島城跡（平成 23・24 年度郭Ⅵ調査 報告第 3 集），広島県教育委員会（2002） 報告書，今治市埋蔵文化財調査報告書第 125 集），今治市教 8) Misakubo-cho Board of Education (ed.): Comprehensive 育委員会（2014） Research Report of Takane Castle (Kuzugo Castle), Misakubo-cho 2) Imabari City Board of Education (ed.): Historical Site Noshima Cultural Heritage Survey Reports Vol.7), Misakubo-cho Board of Castle Ruins (2009-2010 Survey Report for Enclosure Ⅰ/Ⅳ/Ⅴ: Education (2002) (in Japanese) Imabari City Archeological Heritage Survey Reports Vol. 108), 静岡県水窪町教育委員会編：高根城（久頭郷城）総合研究 Imabari City Board of Education (2011) (in Japanese) 報告書（水窪町文化財調査報告書第 7 集），静岡県水窪町教 今治市教育委員会編：能島城跡（平成 21・22 年度郭Ⅰ・ 育委員会（2002） 郭Ⅳ・郭Ⅴ・南部平坦地下海岸調査報告書，今治市埋蔵文 9) Kato, M.: Takane Castle (Kuzugo Castle) from Viewpoint of 化財調査報告書第 108 集），今治市教育委員会（2011） Excavation survey, Misakubo-cho Board of Education (ed.): 3) Imabari City Board of Education (ed.): Historical Site Noshima Comprehensive Research Report of Takane Castle (Kuzugo Castle Ruins (2010-2011 Survey Report for Enclosure Ⅱ : Castle), Misakubo-cho Cultural Heritage Survey Reports Vol.7), Imabari City Archeological Heritage Survey Reports Vol. 119), Misakubo-cho Board of Education, pp237-254 (2002) (in Imabari City Board of Education (2013) (in Japanese) Japanese) 今治市教育委員会編：史跡能島城跡（平成 22・23 年度郭 加藤理文：発掘調査から見た高根城（久頭郷城），静岡県水 Ⅱ（ 第 2・3 次）調査報告書，今治市埋蔵文化財調査報告書 窪町教育委員会編：高根城（久頭郷城）総合研究報告書（水 第 119 集），今治市教育委員会（2013） 窪町文化財調査報告書第 7 集），静岡県水窪町教育委員会， 4) Imabari City Board of Education (ed.): Historical Site Noshima pp237-254（2002） Castle Ruins (2010-2011 Survey Report for Enclosure Ⅲ : Imabari City Archeological Heritage Survey Reports Vol. 112),

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98 広島商船高等専門学校紀要 第40号（2018）

Notes

Note 1) For the outcomes of the survey, see Imabari City Board of Education (ed.) “Historical Site Noshima Castle Ruins” (Imabari Board of Education, 2006-2017).（今治市教育委員会編：史跡 能島城跡，今治市教育委員会，2006-2017） Note 2) A central pillar hole has not been identified in all cases, but most of the seirō-remnants were confirmed to have a central pillar hole in the middle of the 2 ken × 2 ken base and were thus classified as being of the sōbashira-style. Note 3) For more on the Noshima Murakami clan, see Morimoto, S., “The Complete History of the Murakami Privateers” (Shinjinbutsu Ōraisha, 2008).（森本繁：村上水軍全史，新人物 往来社，2008） Note 4) 2 m is equivalent to 6 shaku (尺) and 5 sun (寸). In Japanese architecture of the time, these were the standard units of measurement for the distance between two pillars. Note 5) Among the pillar holes of the taisaki-demaru seirō, the deepest hole is 75 cm. Thus, the structure would presumably have stood at around 7.5 m above ground. Note 6) In cases where the procured wood was of different sizes, it was common practice to modify the depths of the pillar holes accordingly. Note 7) Large fortresses sometimes had multiple seirō, but only in rare cases. Note 8) Examples of times that would have warranted further fortification include 1576, when Noshima Murakami participated in the Battle of Kizugawaguchi (Nobunaga Oda〔織田信長〕 versus Mōri), and when Takakage Kobayakawa approached the fortress after Noshima Murakami refused to support Hideyoshi Toyotomi’s subjugation of Shikoku in 1585. Note 9) Two such structures (SB1 and SB2) are in the honguruwa, one (SB7) was in the kojō, and one was in the shinjō. Note 10) Dobeis and fences (saku〔柵〕) had the same basic structure, but the former presented a solid barrier while the latter did not. Thus, the survey team were unable to determine from the remnant whether it was the dobei or fence. Given that the inhabitants of the fortress anticipated sieges, the outer ramparts probably consisted of the dobei and the inner ramparts the fence. Note 11) Ogurayama Castle was abandoned when the Kikkawa clan relocated their headquarters to Hinoyama Castle (日の山城). Note 12) The seirō erected by the shogunate army during the Shimabara-Amakusa Rebellion (天草・島原の乱) and those temporarily erected in Nijō castle (二条城) and Akō castle (赤穂 城) were restorations.

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