At the western, northern and eastern sides of the palace, there were three rectangular porticos each of which had twelve columns in two rows of six. At the south of the grand hall, a series of rooms were built for storage. Two grand Persepolitan stairways were built, symmetrical to each other and connected to the stone foundations. To protect the roof from erosion, vertical drains were built through the brick walls. In the four corners of Apadana, facing outwards, four towers were built.