Tsukuroumi Castle was a mountain castle that once stood in Takeoka, Futtsu City, Chiba Prefecture. Its history is closely connected with several powerful clans that played important roles in the political struggles of the Kanto region during the Sengoku period, including the Mariyatsu clan, the Kazusa-Takeda clan, and the Satomi clan.
The castle was built by making clever use of the surrounding natural terrain. Its remaining earthworks and other features provide valuable evidence of the region’s medieval history and continue to attract attention as an important cultural heritage site.
Tsukuroumi Castle is generally believed to have been constructed by the Mariyatsu clan, although some historians have proposed different theories about its origins.
Historian Kuroda Motoki has suggested that “Tsukusa-go” (造細郷) in Kazusa Province, which Ashikaga Shigeuji reportedly granted to Takeda Nobunaga, the founder of the Kazusa-Takeda clan and ancestor of the Mariyatsu family, may actually have been a mistaken transcription of “Tsukuroumi-go” (造海郷). Based on this interpretation, Tsukuroumi Castle may have been Takeda Nobunaga’s first base of operations, while the expansion into Mariyatsu Castle and Chonan Castle may have taken place from the following generation onward.
From 1537 onward, Tsukuroumi Castle came under the control of the Satomi clan and played an important role as a frontline military base in the Satomi clan’s struggles against the powerful Hojo clan.
Tsukuroumi Castle is traditionally said to have been built in 1461 by either Mariyatsu Nobuoki or Takeda Nobunaga. In the following decades, the castle repeatedly became involved in conflicts between competing regional powers.
In 1534, a succession dispute broke out between Mariyatsu Nobutaka and Nobumasa. Nobumasa’s son, Nobumasa, took control of Tsukuroumi Castle. In 1537, however, the castle was attacked by forces led by Satomi Yoshiaki, who supported Nobumasa’s rival. The castle eventually surrendered, and members of the Masaki clan, who served the Satomi clan, subsequently took up residence there.
In 1590, following Toyotomi Hideyoshi’s campaign against the Hojo clan, the Satomi clan was reduced to control of Awa Province alone. Tsukuroumi Castle was subsequently abandoned as a castle site.
During the final years of the Edo period, two daiba gun batteries were constructed at the northern and southwestern ends of the former castle grounds. These fortifications were built as part of the coastal defenses of the late Edo period, giving the site a second chapter in its military history long after the castle itself had been abandoned.
Tsukuroumi Castle was built on a highly independent ridge extending from north to south beside the Uraga Channel. Its location provided formidable natural defenses: the western side faced the Uraga Channel, while the northern side was protected by the Shirakogawa River.
Four major kuruwa, or fortified enclosures, were arranged along the main ridge. Additional enclosures were positioned along subsidiary ridges and at the upper sections of valleys, creating a defensive network that took full advantage of the mountainous terrain.
Although the eastern side of the castle site is less rugged than the western side, defensive measures were incorporated along the ridge beside Mihashira Shrine and along ridgelines connecting the castle with the surrounding area.
These features are thought to have protected the main approach from Toro-zaka Daishi as well as residential compounds associated with Enmeiji Temple and Mihashira Shrine.
Near the base of the main ridge is an area known as Kide-ne, where a lower fortified enclosure, or koshikuruwa, was constructed as part of the castle’s defensive system.
A number of castle remains survive on the mountaintop in remarkably recognizable form, including dry moats, stone walls, earthen embankments, and wells. These features provide valuable clues about how the castle was constructed and defended during the medieval period.
The site also contains traces of the coastal gun batteries built during the late Edo period. The coexistence of these later military structures with the earlier castle remains makes Tsukuroumi an especially interesting historical site, showing how the strategic importance of the location continued into the nineteenth century.
Access to the Tsukuroumi Castle ruins is not extensively developed or maintained as a conventional tourist site. Visitors are therefore advised to check maps and the terrain carefully before setting out.
Because the site is located in a mountainous area and the route may be difficult to follow, it is recommended that visitors obtain up-to-date information from a local tourist information center before attempting to reach the ruins.
Tsukuroumi Castle is a fascinating mountain castle site associated with major powers of the Sengoku period, including the Mariyatsu, Kazusa-Takeda, and Satomi clans. Its surviving remains offer a glimpse into the military landscape of medieval Kanto.
The castle’s strategic use of natural terrain, together with the traces of coastal defenses added centuries after the castle was abandoned, reveals how the site’s military significance changed over time.
For visitors interested in Japanese castles and history, Tsukuroumi Castle provides an opportunity to explore a lesser-known historical site and imagine the struggles for power that once unfolded across the Boso Peninsula.