In the Edo period, the Seto Inland Sea was one of the busiest transport lines in Japan. It was a part of a navigational route around Japan's islands via the Sea of Japan. Many ships navigated from its coastal areas to the area along the Sea of Japan. Major ports in the Edo period were Osaka, Sakai, Shimotsui, Ushimado, and Tomonoura. The Seto Inland Sea also served many daimyōs in the western area of Japan as their route to and from Edo, to fulfill their obligations under sankin-kōtai. Many used ships from Osaka. Thanks to transport through the Seto Inland Sea, Osaka became the economic center of Japan. Each han had an office called Ozakayashiki in Osaka. These Ozakayashiki were among Japan's earliest forms of banks, facilitating domestic trade and helping to organize the income of the daimyo, which was in the form of koku, giant bales of rice.
