Sakai is a city located in Osaka Prefecture, Japan. It has been one of the largest and most important seaports of Japan since the medieval era. Sakai is known for its kofun, keyhole-shaped burial mounds dating from the fifth century. The kofun in Sakai include the largest grave in the world by area, Daisen Kofun. Once known for swords, Sakai is now famous for the quality of its cutlery.