The Siege of the Ishiyama Honganji was the longest siege in Japanese history, lasting eleven years. The Ikko-ikki, mobs of warrior monks and peasants, controlled the Ishiyama Honganji fortress, and were among the last to stand in the way of Oda Nobunaga's bid to conquer all of Japan. Oda had fought the Ikki before, crushing their armies of Mikawa Province and other areas, and their twin fortresses of Ishiyama Honganji and Nagashima were their last bastions of strength. He sieged both fortresses simultaneously, attacking Ishiyama in August 1570 and Nagashima in 1571. The siege of the Ishiyama would last until August of 1580, when the Abbot Kosa was convinced to surrender.

In August 1570, Oda Nobunaga left his castle in Gifu with 30,000 troops, and ordered the building of fortresses around the Ishiyama. On September 12th, the Ikko-ikki launched a midnight stealth attack with 3000 arquebusiers, destroying several of these forts, and pushing Oda's army back. While Oda himself focused on the sieges of the Nagashima fortress and other campaigns, his armies remained camped out, assigned to monitor the Ikki's fortress, and take it if they could.

In April 1576, Oda's army attacked with 3,000 men under the command of Akechi Mitsuhide and Araki Muneshige . By now, 51 outposts had been built around the central fortress, many equipped with arquebus squads. The attackers were quickly repelled by 15,000 defenders. Oda Nobunaga was forced to revise his tactics, and began to attack the outposts, and the supporters of the Ikki. He sent Toyotomi Hideyoshi to head an assault on the monk's fortress at Negoroji .

After reducing the threat from the Ikki's supporters, Oda attempted to starve out the fortress. This was no easy task, however, because the Ishiyama fortress sat on the coast, which was guarded by the fleet of the Mori clan, masters of naval combat, and Oda's dire enemies. In 1575, the fortress was in urgent need of supplies, and the Abbot Kosa was ready to begin peaceful overtures with Nobunaga, to end the siege. But the ousted Shogun, Ashikaga Yoshiaki sent a letter to Mori Terumoto, asking for his aid in supplying the cathedral fortress. Nobunaga enlisted Kuki Yoshitaka to set up a blockade and disrupt the fortress' supply lines. In August 1576, in the first battle of Kizugawaguchi, the blockade failed. But Kuki Yoshitaka returned two years later with massive new battleships and, in the second battle of Kizugawaguchi, he broke the Mori supply lines for good.

By now the siege was beginning to swing in Oda Nobunaga's favor. The majority of the Ikki's allies were already inside the fortress with them, so they had no one to call on for aid. Uesugi Kenshin, one of Nobunaga's strongest enemies, and therefore among the Ikki's strongest allies, died in 1578, and the Mori clan lost their castle at Miki in 1580. Between 1578 and 1580, the Ikki sallied forth from the fortress many times under the leadership of Shimotsuma Nakayuki , to face Oda's armies.

But by April of 1580, the defenders were nearly out of ammunition and food. The Abbot Kosa held a conference with his colleagues, and shortly afterwards received a message from the Emperor himself, asking that the Ikki surrender. It was no secret that this letter had been prompted by Nobunaga, but that would not change the power of an Imperial request; Kosa surrendered several weeks later, and fighting finally ended a few months after that, in August, 1580.

Nobunaga spared the lives of many of the defenders, including Shimotsuma Nakayuki , but burned the fortress to the ground. Three years later, Toyotomi Hideyoshi would begin construction on the same site, building Osaka Castle, which still stands today.

References

• Sansom, George (1961). "A History of Japan: 1334-1615." Stanford: Stanford University Press.
• Turnbull, Stephen (2003). 'Japanese Warrior Monks AD 949-1603'. Oxford: Osprey Publishing.