While Europe's royal houses are measured in centuries, Japan's is measured in millennia. The Yamato dynasty, considered the oldest unbroken hereditary monarchy in the world, stretches over 2,000 years and 125 emperors - a figure beside which every crown in Europe looks like a recent invention. And in the heart of Tokyo, on the foundations of the old Edo castle, stands the palace that guards that line.

The Imperial Palace occupies 150 hectares with four large sectors - a main building of reinforced concrete with a traditional Japanese interior, six wings, museums, libraries, and the Fukiage garden where the most private quarters and three sacred shrines are located. A large part of the original structure was damaged in the bombings during the Second World War and later rebuilt. Today it is home to Emperor Naruhito and Empress Masako.

But behind the splendour hides a problem Japan has refused to solve for decades. The succession law of 1947 allows only a male descendant to take the throne. This means that Princess Aiko, the emperor's only child, is excluded from the succession - simply because she is a woman. The entire future of the world's oldest dynasty now hangs on one teenager: the 19-year-old Prince Hisahito, the only male heir.

Here lies the irony that the palace, with all its shrines, cannot hide. An institution that prides itself on two thousand years of continuity risks breaking that continuity over a rule less than a century old. The cherry blossom in the courtyard symbolises transience and renewal - but renewal, it seems, is allowed only to nature, not to the crown itself. How many traditions in the Balkans are defended by the very people who lose most from them?