Tokyo, officially Tokyo Metropolis, is one of the 47 prefectures of Japan and located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, and total over 8 million people. The population of the prefecture exceeds 12 million. Tokyo is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family. Tokyo was originally known as Edo, meaning estuary. Its name was changed to Tokyo (Tōkyō: tō (east) + kyō (capital)) when it became the imperial capital in 1868. During the early Meiji period, the city was also called "Tōkei", an alternative pronunciation for the same Chinese characters representing "Tokyo". Some surviving official English documents use the spelling "Tokei". This pronunciation is now obsolete. Tokyo was originally a small fishing village named Edo. In 1457, Ōta Dōkan built Edo Castle. In 1590, Tokugawa Ieyasu made Edo his base and when he became shōgun in 1603, the town became the center of his nationwide military government. During the subsequent Edo period, Edo grew into one of the largest cities in the world with a population topping one million by the 18th century. It became the de facto capital of Japan even while the emperor lived in Kyoto, the imperial capital. After about 263 years, the shogunate was overthrown under the banner of restoring imperial rule.