<P> Although the Emperor has been a symbol of continuity with the past, the degree of power exercised by the Emperor has varied considerably throughout Japanese history . In the early 7th century, the Emperor had begun to be called the "Son of Heaven" (天子, tenshi, or 天子 様 tenshi - sama). </P> <P> The title of Emperor was borrowed from China, being derived from Chinese characters and was retroactively applied to the legendary Japanese rulers who reigned before the 7th--8th centuries AD . </P> <P> According to the traditional account of the Nihon Shoki, Japan was founded by Emperor Jimmu in 660 BC . Modern historians agree that the Emperors before the possible late 3rd century AD ruler known traditionally as Emperor Ōjin are legendary . Emperor Ankō of the 5th century AD, traditionally the 20th emperor, is the earliest generally agreed upon historical ruler of all or a part of Japan . The reign of Emperor Kinmei (c. 509--571 AD), the 29th emperor, is the first for which contemporary historiography is able to assign verifiable dates; however, the conventionally accepted names and dates of the early emperors were not to be confirmed as "traditional" until the reign of Emperor Kanmu (737--806), the 50th sovereign of the Yamato dynasty . </P> <P> Archaeological information about the earliest historical rulers of Japan may lie within the ancient tombs known as kofun, constructed between the early 3rd century and the early 7th century AD . However, since the Meiji period, the Imperial Household Agency has refused to open the kofun to the public nor to archaeologists, citing their desire not to disturb the spirits of the past Emperors . In December 2006, the Imperial Household Agency reversed its position and decided to allow researchers to enter some of the kofun with no restrictions . </P>

Who were the first family to be recognized as emperors of japan