Persian columns or Persepolitan columns are the distinctive form of column developed in the Achaemenid architecture of ancient Persia, probably beginning shortly before 500 BCE. They are mainly known from Persepolis, where the massive main columns have a base, fluted shaft, and a double-animal capital, most with bulls. Achaemenid palaces had enormous hypostyle halls called apadana, which were supported inside by several rows of columns. The Throne Hall or "Hall of a Hundred Columns" at Persepolis, measuring 70 × 70 metres was built by the Achaemenid king Artaxerxes I. The apadana hall is even larger. These often included a throne for the king and were used for grand ceremonial assemblies; the largest at Persepolis and Susa could fit ten thousand people at a time. The Achaemenids had little experience of stone architecture, but were able to import artists and craftsmen from around their empire to develop a hybrid imperial style drawing on influences from Mesopotamia, Egypt and Lydia in Anatolia, as well as Elam in Persia itself. The style was probably developed in the Palace of Darius in Susa, but the most numerous and complete survivals are at Persepolis, where several columns remain standing. Imperial building in the style stopped abruptly with the invasion by Alexander the Great in 330 BCE, when Persepolis was burned down. Description The forms of the columns and capitals vary somewhat between different buildings. Generally the capitals are carved with two heavily decorated back-to-back animals projecting out from the column. These function as brackets to support the architrave or roof timbers, while the flat backs of the animals support timbers running at right angles (see the reconstruction in the Louvre below). As they project the animals may be called protomes. The bull is the most common animal, but there are also lions, bulls with the head of a man in the style of the Assyrian lamassu, and griffins with the heads of eagles and the bodies of lions. The bulls and lions may reflect the symbolism around Nowruz, the Persian New Year at the spring equinox, of an eternally fighting bull personifying the moon, and a lion personifying the Sun. This was the day when tributary nations presented their annual tribute to the king, as depicted in the stairway reliefs at Persepolis, and it has been suggested that Persepolis was specifically built for Nowruz celebrations. The capital is much longer than in most other styles