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 Empire
The Achaemenids thereafter consolidated areas firmly under their control. It was Cyrus the Great and Darius the Great who, by sound and far-sighted administrative planning, brilliant military manoeuvring, and a humanistic world view, established the greatness of the Achaemenids and, in less than thirty years, raised them from an obscure tribe to a world power. It was during the reign of Darius the Great (Darius I) that Persepolis was built (518–516 BC) and which would serve as capital for several generations of Achaemenid kings. Ecbatana ("Hagmatāna" "City of Gatherings", modern: Hamadan) in Media was greatly expanded during this period and served as the summer capital.