The or the Straits of Shimonoseki is the stretch of water separating two of Japan's four main islands. On the Honshu side of the water is Shimonoseki (, which contributed "Kan" to the name of the strait) and on the Kyushu side is Kitakyushu, whose former city and present ward, Moji , gave the strait its "mon" . The straits silt up at the rate of about 15 centimetres per annum, and dredging has made it possible to build the New Kitakyushu Airport at low cost.