Emperor Nintoku
By the Kofun period (250-538 CE), Osaka developed into a hub port connecting the region to the western part of Japan. The port of Naniwa-tsu was established and became the most important in Japan. Trade with other areas of the country and the Asian continent intensified. The large numbers of increasingly larger keyhole-shaped Kofun mounds found in the plains of Osaka are evidence of political-power concentration, leading to the formation of a state. The findings in the neighboring plains, including the mausoleum of Emperor Nintoku was discovered nearby in Sakai testify to the status of imperial city that Ōsaka had reached. Four of these mounds can be seen in Ōsaka, in which important members of the nobility are buried. They are located in the southern districts of the city and date back to the 5th century. A group of megalithic tombs called Mozu Tombs are located in Sakai, Osaka Prefecture.