The Ii Family and Hikone Domain 彦根城博物館展示解説シート　仮）井伊家と彦根藩

The Ii were supporters of the shogun Tokugawa Ieyasu (1543–1616) during his unification of Japan, and they were granted considerable power within the Tokugawa government. When the shogun was forced to delegate administrative matters, he turned to the tairō, a senior official who functioned like a prime minister. Ii Naotaka (1590–1659) was made tairō in 1632, and of the subsequent nine tairō who served the shogun during the Tokugawa period, four were members of the Ii family.

Hikone Domain

Hikone domain was established in 1600 as the han of Ii Naomasa (1561–1602). He was awarded the position of daimyo in recognition for his performance that same year at the Battle of Sekigahara, a crucial battle whose outcome is viewed as having cemented the unification of Japan. Hikone was important both commercially and strategically as a rich agricultural area situated on Lake Biwa and a major stop on the Nakasendō, one of two roads that connected the capital of Edo to western Japan. It was also a wealthy domain with an income of approximately 300,000 koku, or enough rice to feed 300,000 adult males for a year.

Hikone Castle

The Ii family began building Hikone Castle in 1604 on orders from the shogunate. Tokugawa Ieyasu wanted to establish defenses against a possible attack by anti-shogunate daimyo in the western part of the country. The main parts of the castle, including the keep, were completed in 1607. Construction was temporarily halted while the Ii family assisted Ieyasu in securing control of the country with the Siege of Osaka (1614–1615), and the entire castle complex, including its moats, was completed in 1622.