Darius the first, the great Achaemenian king, created  reorganized and unified an empire which eventually was larger and more efficiently ruled than any other the ancient world had seen yet. Darius conceived Persepolis, its unmatched splendour still evident today, despite the ravages of foreign invaders and centuries of exposure, as the spiritual hub of the empire. The building program began by Darius the first (486-522 BC) was carried by his two immediate successors. The most important building at Persepolis were crowded onto a terrace of natural rock that rises 12 meters above the plain on three sides and abuts a low mountain on the forth side. There are about fifteen major buildings, including the Apadana, the Hall of Hundred Columns, the Gate House of Xerxes, the Treasury, the 'Harem', the so called central building and the majestic palaces of Darius the Great ,Xerxes, Artaxerxes I and Artaxerxes III.Persepolis was the side to which the Archaemenid kings came to celebrate the Iranian New Year, and the achievements of their ancestors in religious ceremonies, to receive foreign delegations, and to be buried, until it was burnt to the ground by Alexander of Macedonia in 330 B.C. The existing remains consist of stone columns with elaborate bases and capitals, stone doors and window jambs, and facades and staircases ,many with splendid bas-reliefs and reliefs sculptures. They make Persepolis one of the most impressive sites, not just in Iran but in the whole of the ancient world.