Hokkaiō (help·info) (北海道, ? literally "North Sea Circuit", Ainu: Ainu Mosir), formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island and the largest, northernmost of its 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaidō from Honshū, although the two islands are connected by the underwater Seikan Tunnel. The largest city on Hokkaidō is its capital, Sapporo, which is also its only ordinance-designated city.