beneath it, until the opposite courses touch and form one. [Illustration: Fig. 4.--Corbelled vaulting at Mugheir (after Taylor).] It was, then, as it seems, the Chaldæans who invented the vault;[10] the want of timber compelled them in early times to contrive to defend themselves at once against the heavy rains and the ardour of a torrid sun; the creation of the vault was in their case instinctive and spontaneous. They raised, two or three thousand years before our era, vaults and domes like those which are built to this day by the rudest masons at Mosoul or Bagdad. No doubt the present state of the Chaldæan ruins and the insufficient explorations which have been undertaken among them do not enable us to say whether these Proto-Chaldæans knew every kind of vault, as the Assyrians did in the age of the Sargonids, or the Babylonians at the epoch of Nebuchadnezzar; but the remarkable perfection observed in their monumental structures, and in the very manufacture of the bricks, are so many arguments in favour of the inference that the palaces and houses of the Chaldæans in the time of Gudea were surmounted, for the most part, by semicircular vaults or by cupolas, as were later, according to Strabo,[11] the houses of the Babylonians. The vaults supported a terrace formed of clay; this layer of earth would be less thick over rooms roofed only with a ceiling of palm-beams and reed-matting. The ascent was by staircases, an example of which seems to have been found in the palace at Tello.[12] While clearing away the material accumulated between the courts A and B, the workmen employed by the French explorer came into contact (at the point H) with a structure of baked brickwork, which proves that the Chaldæans at the remotest epoch had already invented one of the most interesting and characteristic elements of their architecture--the _zikkurat_ or staged tower. The lower layers in the palace of Gudea alone exist, and are composed of two solid masses in stages one above the other. In its present condition the upper terrace is a mass 26 ft. square, 13 ft. less on all sides than the lower stage; perhaps there still exists a third and lower step, which has not been reached by the soundings, which are imperfect at this point. The _zikkurat_ of Tello was not in any case so lofty or so important a structure as those of the Ninevite palaces or those represented by the ruins of Babil or Birs Nimroud at Babylon. It was even much less considerable than that which Taylor observed at Abu Shahrein, and which was equally old. These towers always had, from the first, seven stages, each painted of a different colour, and connected with the worship of the sun (Samas), the moon (Sin), and the five planets of the astronomical system of the Chaldæans.