Imperial Household Agency has given researchers the permission to study 11 royal tombs, the graves of ancient emperors, sealed centuries ago, in a move that may shed light on the enigmatic origins of Japan's imperial family.

The secretive Imperial Household Agency has until now refused to let the public, and even scholars, enter the old tombs, saying that the spirits of ancient emperors should not be disturbed. But after a petition by the Japanese Archaeological Association and other scholars in 2005, the government has agreed to give them limited access to the graves.

A small number of archaeologists will be allowed to enter only the outer fringes of the tombs, and will not be allowed to excavate. Archaeologists say that inspecting the tombs could explain more on the origins of the country's imperial family, the world's oldest surviving line - a sensitive topic in Japan, where until 60 years ago the emperor was worshipped as the descendant of an ancient goddess of the Sun.

The late Emperor Hirohito broke with that tradition by giving up his divine status in 1945, after Japan's defeat in World War II.

But the myth that Japan's 125 emperors descended from the sun goddess Amaterasu Omikami of Japan's native Shinto religion still holds among rightists. Suggestions by some scientists that the imperial line originated elsewhere - for example, on the Korean peninsula - have been regarded as an insult to the Japanese people.

Among the tombs to investigat, there is the one belonging to the Emperor Nintoku (photo), who is thought to have died in the late fourth or early fifth century.