The Shinano River (信濃川 Shinano-gawa) is the longest and largest river in Japan. It flows from Nagano Prefecture to Niigata Prefecture. It is called the Chikuma River (千曲川 Chikuma-gawa) in Nagano Prefecture. The river rises from Mount Kobushi on the border of Saitama, Yamanashi and Nagano, and flows northwest to meet the Sai River from Matsumoto. Kawanakajima (川中島), the junction of the Chikuma and the Sai, is the historic site of the Battles of Kawanakajima. It turns to the northeast and empties into the Sea of Japan at Niigata City. In 1922, the Ōkōzu Canal (大河津分水路 Ōkōzu Bunsuiro) was built to defend Niigata from floods. It enabled the Niigata Plains to be filled with rich rice fields. The name Chikuma was given to two Imperial Japanese Navy cruisers.