Siege of Kōzuki Castle

What Happened

The siege of Kōzuki Castle (上月城の戦い, Kōzuki-jō no Tatakai) was fought from 24 May to 6 August 1578. The attacking army belonged to Mōri Terumoto, one of the most powerful daimyō (大名, territorial lords) of western Japan. The castle's defender was Amago Katsuhisa, a member of the Amago clan who had been installed there the previous year.

The Mōri invested the castle and pressed the garrison through the summer. On 6 August 1578 the castle fell. Amago Katsuhisa took his own life rather than surrender. His general Yamanaka Yukimori, celebrated for his loyalty, was taken alive and executed.

The castle stood at the site now marked by the coordinates 34.9770833, 134.3242222, in Harima Province. The fighting took place in the sixth year of the Tenshō era (天正, Tenshō), during the Azuchi–Momoyama period, the decades of unification under Oda Nobunaga and his successors.

Background

Kōzuki Castle had been captured by Toyotomi Hideyoshi in 1577, the year before the siege. Hideyoshi was then one of Oda Nobunaga's leading commanders, pushing Nobunaga's authority westward along the Inland Sea coast. Rather than hold Kōzuki directly, Hideyoshi entrusted it to Amago Katsuhisa.

The Amago were the old ruling house of Izumo in western Japan, and the Mōri had destroyed their power decades earlier. Restoring an Amago heir to a castle on the Mōri frontier was a direct provocation. It gave Nobunaga a legitimate local claimant to set against Mōri Terumoto, and it gave Amago Katsuhisa a chance to revive his family's fortunes.

The siege was part of the Chūgoku Campaign, the long struggle between Nobunaga's forces and the Mōri for control of the Chūgoku region. Kōzuki was one of its forward positions, and the Mōri could not leave it in enemy hands.

Why It Mattered

The fall of Kōzuki removed Nobunaga's foothold in the Mōri borderlands and ended the Amago restoration as a political project. Amago Katsuhisa's death closed the line of claimants the Oda had been backing, and the Mōri recovered the ground they had lost in 1577.

The deaths of Katsuhisa and Yamanaka Yukimori became famous in later Japanese storytelling. Yamanaka in particular was remembered as the model of a retainer who stayed loyal to a doomed lord, and his execution gave the siege a lasting place in the popular memory of the period.

Strategically, the defeat shifted the Chūgoku Campaign back toward a war of attrition. Nobunaga's forces would not break Mōri resistance until the campaigns of the early 1580s, and Nobunaga himself was killed at Honnō-ji in 1582 before the region was settled.

The Name in Japanese

The Japanese name is 上月城の戦い, read in kana as こうづきじょうのたたかい, and romanised as Kōzuki-jō no Tatakai.

Breaking it down:

• 上 — read here as こう (kō). The character means "above" or "up". In this place name it is read with its Chinese-derived on reading rather than its native Japanese reading.
• 月 — read here as づき (zuki). The character means "moon" or "month". On its own it is read つき (tsuki); after another character it voices to zuki, which is why the name is Kōzuki and not Kōtsuki.
• 城 — read here as じょう (jō). The character means "castle". It is the standard element in Japanese castle names, as in Osaka-jō or Himeji-jō.
• の — the possessive particle, written in kana rather than kanji. It links the castle name to the word that follows, functioning like "of" in English.
• 戦 — read here as たたか (tataka), the stem of the verb tatakau, "to fight". The character means "war", "battle" or "combat".
• い — kana completing the reading たたかい (tatakai), a noun meaning "battle" or "fight".

So the whole name means, plainly, "the battle of Kōzuki Castle". Note that 城 appears in the castle's name and 戦い supplies the word "battle"; Japanese place-name compounds of this kind are read as a single unit, which is why the romaji runs together as Kōzuki-jō no Tatakai.

The long vowel in Kōzuki is worth watching. The macron over the first o marks a vowel held for two beats, not a stressed syllable. English speakers who write "Kozuki" or "Kozuki Castle" lose that distinction.

Key Figures

Amago Katsuhisa commanded the defence of Kōzuki Castle. He was installed there by Toyotomi Hideyoshi in 1577 as the Oda-backed claimant to the Amago inheritance. He took his own life when the castle fell on 6 August 1578.

Mōri Terumoto led the attacking army. He was the head of the Mōri clan and the dominant power in western Japan, and the siege formed part of his long resistance to Oda Nobunaga's westward expansion.

Yamanaka Yukimori served as Amago Katsuhisa's general and was known for his loyalty to the Amago house. He was captured when Kōzuki fell and was executed.

Toyotomi Hideyoshi had taken Kōzuki Castle in 1577 and placed Amago Katsuhisa in charge of it. He was one of Oda Nobunaga's principal commanders during the Chūgoku Campaign.

Oda Nobunaga was the overlord whose westward push against the Mōri produced the campaign in which the siege took place.