Persepolis
Darius I built the greatest palace at Persepolis on the western side of platform. This palace was called the "Apadana". The King of Kings used it for official audiences. The work began in 518 BC, and his son, Xerxes I, completed it 30 years later. The palace had a grand hall in the shape of a square, each side long with seventy-two columns, thirteen of which still stand on the enormous platform. Each column is high with a square Taurus (bull) and plinth. The columns carried the weight of the vast and heavy ceiling. The tops of the columns were made from animal sculptures such as two-headed lions, eagles, human beings and cows (cows were symbols of fertility and abundance in ancient Iran). The columns were joined to each other with the help of oak and cedar beams, which were brought from Lebanon. The walls were covered with a layer of mud and stucco to a depth of 5 cm, which was used for bonding, and then covered with the greenish stucco which is found throughout the palaces.
Persepolis
The function of Persepolis remains rather unclear. It was not one of the largest cities in Persia, let alone the rest of the empire, but appears to have been a grand ceremonial complex, that was only occupied seasonally; it is still not entirely clear where the king's private quarters actually were. Until recent challenges, most archaeologists held that it was especially used for celebrating Nowruz, the Persian New Year, held at the spring equinox, and still an important annual festivity in modern Iran. The Iranian nobility and the tributary parts of the empire came to present gifts to the king, as represented in the stairway reliefs.