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.
Achaemenid architecture
Persepolis is the Latinized version of the Old Persian name, "Parsa" literally meaning the "city of Persians." Another spectacular achievement of the Achaemenids, Persepolis became one of the four capitals of the empire. Initiated by Darius the Great around 518 B.C.E., it would grow to become a center for ceremonial and cultural festivities, a center for dignitaries and visitors to pay homage to the king, a private residence for the Persian kings, a place for satraps to bring gifts for the king in the Spring during the festival of Nowruz, as well as a place of governance and ordinance. Persepolis's prestige and grand riches were well known in the ancient world, and it was best described by the Greek historian Diodorus Siculus as "the richest city under the sun".