Darius, the Persian ruler in 515 BC needed a ceremonial capital. This resulted in the creation of one of the great citadels of all times, Persepolis. It comprises of various monumental buildings on a big artificial stone terrace about 1,480 by 1,000 ft. A wide and shallow double staircase was constructed for horses to climb from the plains to the top of the terrace. Also, the head of the staircase is encompassed with the Gate of Xerxes, a gatehouse safeguarded by huge carved stone bulls.