type of burial mounds dating from this era. During the Kofun period, elements of Chinese culture continued to influence culture in the Japanese archipelago, both through waves of migration and through trade, travel, and cultural change. Archaeological evidence indicates contacts between the mainland and Japan also during this period. Most scholars believe that there were massive transmissions of technology and culture from China via Korea to Japan which is evidenced by material artifacts in tombs of both states in the Proto–Three Kingdoms of Korea and Kofun period, as well as the later wave of Baekje refugees to Yamato. Archaeological records and ancient Chinese sources Book of Song indicate that the various tribes and chiefdom of the Japanese Archipelago did not begin to coalesce into more centralized and hierarchical polities until 300 (well into the Kofun period), when large tombs begin to appear while there were no contacts between the Wa and China. Some describe the "mysterious century" as a time of internecine warfare as various local monarchies competed for hegemony on Kyūshū and Honshū. Japan of the Kofun age was positive in the introduction of Chinese culture. Several kinds of goods were imported. Books from China were one of the most important trade goods. Chinese philosophy that had been introduced in this era, had a big influence on the history of Japan. Decorated bronze mirrors (Shinju-kyo) were imported from China. Japan imported iron from Korean peninsula until the latter half of the 6th century. In this period, Baekje received military support from Japan. According to the Samguk Sagi, King Asin of Baekje sent his son Jeonji to Japan in 397 and King Silseong of Silla sent his son Misaheun to Japan in 402 in order to solicit military aid. Kofun tombs Kofun (古墳, "old tomb") are burial mounds which were built for the people of the ruling class during the 3rd to 7th centuries. The Kofun period takes its name from these distinctive earthen mounds which are associated with the rich funerary rituals of the time. The mounds contained large stone burial chambers. Some are surrounded by moats. Kofun came in many shapes, with round and square being the simplest. A distinct style is the keyhole kofun (前方後円墳 zenpō kōen fun), with its square front and round back. Many kofuns were natural hills, which might have been sculpted to their final shape. Kofun range in size from several meters to