Siege of Oshi

What Happened

In the summer of 1590, a Toyotomi army under Ishida Mitsunari (石田三成, いしだ みつなり) laid siege to Oshi Castle (忍城, おしじょう) in Musashi Province, in what is now Saitama Prefecture. The castle was held for the Hōjō clan by Narita Nagachika (成田長親, なりた ながちか), the lord of the Oshi domain. The siege took place in the eighteenth year of the Tenshō era (天正, てんしょう), during the Azuchi–Momoyama period.

The castle stood on low, wet ground surrounded by marsh and rice paddies, which made a direct assault difficult. The Toyotomi force attempted to flood the defenders out by damming the nearby rivers and diverting water against the castle. The water rose, but the castle held. Accounts of the siege describe the defenders moving about the flooded approaches by boat and keeping the garrison supplied, while the besieging army struggled in the waterlogged ground.

Oshi did not fall to assault. The castle was still in Hōjō hands when news arrived that the Hōjō clan's main stronghold, Odawara, had surrendered to Toyotomi Hideyoshi (豊臣秀吉, とよとみ ひでよし). With the Hōjō cause lost, the garrison gave up the castle. The siege is remembered as a case of a small castle outlasting a far larger army.

Background

By 1590 Toyotomi Hideyoshi had unified most of Japan under his authority. The Hōjō clan, based in the Kantō region of eastern Japan, remained outside his control. In the spring of 1590 Hideyoshi launched a massive campaign against them, moving his forces east and concentrating them on the Hōjō capital at Odawara.

Oshi Castle was one of the Hōjō outposts in the Kantō plain, guarding the northern approaches to the Hōjō heartland. As Hideyoshi's commanders fanned out across the region to reduce the Hōjō's subsidiary castles, the task of taking Oshi fell to Ishida Mitsunari. Mitsunari was one of Hideyoshi's senior administrators as well as a field commander, and the siege became associated with his name.

The castle's position in marshy lowland shaped the whole operation. The ground was poor for cavalry and for massed infantry, and the wet terrain made the castle hard to approach and hard to undermine. The flooding attempt that followed was an effort to turn that terrain against the defenders.

Why It Mattered

The siege of Oshi was one engagement within the wider campaign that ended Hōjō power. The surrender of Odawara in 1590 brought the Kantō region under Toyotomi control and completed Hideyoshi's unification of Japan. Oshi's resistance did not change that outcome, but it delayed the reduction of the region's outlying castles.

The siege is remembered for the disproportion between the two sides. A single castle on marshy ground held out against a much larger army, and the flooding scheme failed to force a surrender. The castle changed hands only after the war itself had been decided elsewhere.

For Ishida Mitsunari, the siege became one of the episodes attached to his military reputation. He went on to command the western coalition at the Battle of Sekigahara in 1600, and his career before that battle is often read through engagements such as Oshi.

The Name in Japanese

The Japanese name of the siege is 忍城の戦い. Its kana reading is おしじょうのたたかい, and its romaji is Oshi-jō no tatakai.

Breaking it down character by character:

• 忍 — read おし (oshi) in this name. The character means "endure", "conceal" or "stealth". As a place name it is written with this single character, and the reading おし is specific to the place; the same character read on its own as a common word is しのぶ (shinobu), "to endure" or "to hide".
• 城 — read じょう (jō) here, from しろ (shiro), "castle". It appears in the compound 忍城 (おしじょう, Oshi-jō), "Oshi Castle". The same character is the standard element in Japanese castle names, as in 大坂城 (おおさかじょう, Ōsaka-jō).
• の — the possessive and linking particle, read の (no). It joins "Oshi Castle" to "battle", giving "the battle of Oshi Castle".
• 戦 — read たたかい (tatakai), "battle" or "war". It is the first character of 戦争 (せんそう, sensō), "war", and of 合戦 (かっせん, kassen), "battle".
• い — the final kana of たたかい, completing the reading of 戦い. The verb behind it is 戦う (たたかう, tatakau), "to fight".

So the full name parses as 忍城 (Oshi Castle) + の (of) + 戦い (battle): "the battle of Oshi Castle". Note that the castle's name is written with the character for "endurance", a fitting choice for a garrison that held out through a flooding.

Key Figures

Ishida Mitsunari (石田三成, いしだ みつなり) commanded the Toyotomi force at Oshi. A senior retainer of Toyotomi Hideyoshi, he combined administrative work with military command, and the siege of Oshi is one of the operations associated with him during the 1590 campaign. He later led the western army at Sekigahara in 1600.

Narita Nagachika (成田長親, なりた ながちか) held Oshi Castle for the Hōjō. Under his command the garrison withstood the siege and the flooding of the surrounding ground, and the castle was given up only after the Hōjō surrender at Odawara.

Toyotomi Hideyoshi (豊臣秀吉, とよとみ ひでよし) directed the 1590 campaign against the Hōjō. His forces reduced the Hōjō's castles across the Kantō, and the fall of Odawara ended the war in which the siege of Oshi took place.