89 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 - 1 - 90 広島商船高等専門学校紀要 第40号（2018） 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 - 2 - 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) - 3 - 92 広島商船高等専門学校紀要 第40号（2018） sōbashira-style earthfast pillar structure (Figure 3).