Overview

The Sky Castle of Awaji Island

Sumoto Castle is a mountain castle built atop Mount Mikuma, which rises to 133 meters in the central part of Awaji Island, Hyogo Prefecture. It is characterized by its magnificent location, commanding beautiful views of the Seto Inland Sea and Awaji Island. The existing stone walls were extensively renovated in the early Edo period (Keichō era), and the orderly construction technique of "nurizumi" (布積み) preserves the technical standards of early-modern castle architecture to this day. From the donjon platform, panoramic views spread across the paddy fields of Awaji Island and the straits. On clear days, one can see Shōdoshima and Shikoku across the water. It has become a popular tourist destination known as the "Sky Castle."

The Age of Miyoshi and Atagi

Sumoto Castle's predecessor is said to have been established in the early Sengoku period by Atagi Fuyuyasu, a member of the Miyoshi clan. Atagi Fuyuyasu was the brother of Miyoshi Chōkei and a powerful figure who commanded the naval forces of Awaji and the Kii Channel. Awaji Island's geographic position was a strategic point determining control of the Seto Inland Sea, and Sumoto Castle functioned as its military stronghold. During the Tenshō era (1573–1592), as the Miyoshi declined, control of the castle changed hands. After Toyotomi Hideyoshi's conquest of Awaji, Toyotomi-affiliated warlords were appointed as castle lords.

Wakisaka Yasuharu and Sekigahara

In Tenshō 13 (1585), Wakisaka Yasuharu became lord of Sumoto Castle. Wakisaka Yasuharu is known as one of the 'Seven Spears of Shizugatake' under Toyotomi Hideyoshi, and served as a naval commander during the Bunroku and Keichō campaigns (Korean invasions). At the Battle of Sekigahara in Keichō 5 (1600), he initially sided with the Western Army (Ishida Mitsunari's faction) but is known to have switched to the Eastern Army (Tokugawa Ieyasu's faction) as the battle progressed. After Sekigahara, Wakisaka continued to rule Awaji as lord of Sumoto Castle and undertook major renovations of the castle's stone walls to their present scale. The Wakisaka clan was subsequently transferred to Ōzu Domain in Iyo, and Sumoto Castle was placed under the jurisdiction of the Hachisuka family of Awa Tokushima Domain.

The Stone Walls of the Castle Ruins and "Japan's Oldest Mock Donjon"

The stone walls of Sumoto Castle remain in good condition and are designated as a National Historic Site. The donjon standing on the mountain was constructed as a mock donjon in the early Shōwa period (1928) and attracts unique scholarly interest among castle researchers as "Japan's oldest mock donjon (reinforced concrete construction)." At the base of the mountain, remnants of the early-modern Sumoto Castle (flatland section) also survive, preserving traces of the castle town to this day.

Connection to Swords

Wakisaka Yasuharu, lord of Sumoto, was a celebrated spear-fighter and water general who fought through the invasions of Korea (1592–98), where Japanese swords proved decisive in close combat. As a Seto Inland Sea naval commander, he had ready access to top Bizen and Bichū blades — forged close by across the sea. Water-combat tradition prized shorter, agile swords and tantō for shipboard fighting, and Sumoto's armory reflected these practical demands. Blades associated with Wakisaka's campaigns in Korea represent the living edge of late Sengoku sword culture.

Highlights

Summit stone walls (National Historic Site) — well-preserved Keichō-era coursed masonry

Japan's oldest reinforced-concrete mock donjon (built 1928) — a unique curiosity in castle history

Panoramic Seto Inland Sea views from the summit — islands and straits in every direction

Wakisaka Yasuharu heritage — stronghold of one of Hideyoshi's 'Seven Spears of Shizugatake'

Sumoto castle town — vestiges of the Edo-period lowland castle and historic streetscape

* Image is for illustrative purposes only.

National Historic SiteKansai

Sumoto Castle

洲本城

Lord

Atagi Fuyuyasu / Wakisaka Yasuharu

Era

Built circa 1504–1521 (Eishō era), major reconstruction in the Keichō era (1596–1615)

Designation

National Historic Site

Location

Sumoto City, Hyogo Prefecture (Awaji Island)

Access

About 1 hour by expressway bus from Kobe Sannomiya to Sumoto Bus Center. About 10 min by car from Sumoto IC (Kobe-Awaji-Naruto Expressway). About 15 min walk from Sumoto Bus Center to the castle trailhead.

Sumoto Castle is a historic castle in Kansai dating from the Built circa 1504–1521 (Eishō era), major reconstruction in the Keichō era (1596–1615), whose lord was Atagi Fuyuyasu / Wakisaka Yasuharu.