The architecture of Assyria was not essentially different from that of Babylonia. The Assyrians had brought with them from the lower Euphrates the habit of building in bricks, and continued to use this style, though harder material lay at a less distance from them than from the cities of the Babylonian plain. The temples and the palaces of Asshur, Nineveh, and Chalah consisted for the most part of unburnt brick-slabs, dried in the sun and mixed with straw. This material made it necessary here, as in Babylonia, to make the walls stout, which was also advisable owing to the summer heat. The thickness varies between five and fifteen feet. The stone for the substructure and casing, mostly limestone and shell-stone, was quarried in the adjacent mountains. The buildings were roofed by beams extending from wall to wall: by this necessity the breadth of the rooms was limited. As a rule these are narrow, and the want of breadth is compensated by length. These are the dimensions of the porticoes and galleries which we can trace in the remains of the royal palaces: the great portico of the palace of king Assurnasirpal at Chalah (II. 313) has only a breadth of 35 feet, with a length of 154 feet; the porticoes in the palace of Kuyundshik are from 150 to 180 feet long, and 40 feet in width; the great gallery is only 25 feet broad, but more than 200 feet in length. Yet in the palace of king Sargon at Khorsabad, remains of the bases of pillars have been found. The application of the brick-vaulted roof in the form of pointed and round arches is shown in the narrow passage in the building of Shalmanesar II. at Chalah (II. 323), and in some remains of door-arches at Khorsabad. The pictures of cities in relief also occasionally exhibit arched gateways. The sculptures in the stone slabs of white, grey, and yellow limestone or alabaster, which cover the walls and chambers to a height of 10 or 12 feet, were painted, as is shown by numerous traces of colour upon them.[414] The walls of the chambers above the sculptures, where they did not make way for window lights, were decked with burnt and glazed tiles, sometimes coloured and enamelled; the beams of the roofs were adorned with carved work of wood and ivory, with plates of gold and silver, and precious stones.[415] The outer walls of the palaces must also have been cased with slabs of stone.