In Japanese history, the siege of Ishiyama Hongan-ji — the main stronghold of the Ikkō-ikki movement during Oda Nobunaga’s campaign — is considered the longest, lasting from August 1570 to August 1580.
Initially, in 1496, the monk Rennyo (1415–1499), the ideological and spiritual leader of the Jōdo Shinshū Buddhist sect, withdrew to the mouth of the Yodo River and built a secluded hermitage on the ruins of the ancient Naniwa palace, on the "great slope" — Osaka. This modest retreat quickly grew into a large temple complex, and by 1532, after the destruction of Yamashina Mido, Ishiyama Hongan-ji had become the central fortress-monastery of the Ikkō-ikki, surrounded by the temple town (jinai-machi).
The monastery’s defenses were superbly designed: located on islands at the river’s mouth, surrounded by natural moats (channels) with bridges that could be quickly dismantled in case of attack. Defensive features included earthen ramparts (dorui) with palisades, moats (hori), Koraimon-style gates, and watchtowers. The surrounding jinai-machi acted as the outer perimeter, divided into wards by earthen walls (dobei) and moats. At the center was the island core, fortified with stone walls (ishigaki), dobei, yagura towers, and heavy yaguramon gates—closely resembling a fortified samurai castle.
Instead of a donjon, the central area housed two main halls—Amidado and Goeido—connected by a corridor. These architectural forms remain in use in modern Jōdo Shinshū temples.
The standing garrison consisted of about 100 monks, but at the toll of a bell, up to 10,000 lay followers (monto), including those from Kaga and Echizen provinces, could be summoned. The Mori clan’s navy actively supported the monastery, while Uesugi Kenshin and Takeda Shingen diverted Nobunaga’s forces in the northwest, slowing the siege.
In August 1570, Nobunaga, with a force of around 30,000, initiated the siege, surrounding the monastery with forts. In September, warrior-monks stormed the Kawaguchi and Takadono forts using 3,000 arquebusiers and coordinated volley fire.
The first years were intense, but sea routes kept the monastery supplied until 1576–1578, when Nobunaga shifted focus to maritime blockade using large ships and arquebusiers. After victories in the second Battle of Kizugawaguchi and the death of Uesugi Kenshin, Nobunaga entered the final phase: cutting off allies and capturing outer defenses.
In April 1580, abbot Kōsa (Kennyo) surrendered under imperial order, but the monastery was burned to prevent its capture. Its foundations were destroyed in August. Three years later, in 1583, Toyotomi Hideyoshi built Osaka Castle on the site.
Thus, the siege of Ishiyama Hongan-ji became the largest and longest fortress war in Japanese history, showcasing the defenders' caution and the besiegers’ persistence.
See also
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Siege of Odawara 1590
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Battle of Tenmokuzan
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