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
Scholars agree that it was Darius the Great who initiated the construction and expansion of the Persepolis project, however German archaeologist Ernst E. Herzfeld, believed that it was Cyrus the Great who chose the site for the construction, although it ultimately came down to Darius the Great to finish the construction and create its impressive buildings. Excavations on behalf of the Oriental Institute of Chicago University, headed by Herzfeld in 1931 and later cooperation by Eric F. Schmidt in 1933 led to some of the most impressive uncovering of Achaemenid artifacts, palaces, and structures. Herzfeld felt that the site of Persepolis was made for special ceremonies and was meant to convey the power of the Achaemenid empire to its subject nations.