Sakai (堺市, Sakai-shi) is a city located in Osaka Prefecture, Japan. It has been one of Japan's largest and most important seaports since the medieval era. Sakai is known for its keyhole-shaped burial mounds, or kofun, which date from the fifth century and include Daisen Kofun, the largest grave in the world by area. Once known for swords, Sakai is now famous for the quality of its cutlery. As of 1 January 2022, the city had an estimated population of 819,965, making it the fourteenth most populous city in Japan (excluding Tokyo).