The area around modern Yokkaichi has been settled since prehistoric times. Numerous Kofun period burial mounds have been discovered and the area was one of the battle sites of the Asuka period Jinshin War. However, until the end of the Heian period, the area was sparsely settled, and was only a small port village. The area developed during the Kamakura period and by the Azuchi–Momoyama period, the port was developed and a regular market was open on 4, 14, 24 in each month. Thus, the city is named Yokkaichi because "yokkaichi" means "market on fourth day." After the Honnō-ji Incident during which warlord Oda Nobunaga was assassinated, Tokugawa Ieyasu fled from Yokkaichi port by sea to his castle at Edo. Under the Tokugawa shogunate, Yokkaichi was "tenryō" territory controlled directly by the "shōgun" and administered by a daikan based at the Yokkaichi Jin'ya. Throughout the Edo period, the area prospered as Yokkaichi-juku, the forty-third station on the Tōkaidō highway connecting Edo with Kyoto. However, the city was largely destroyed by the Ansei great earthquakes.