206 HISTOKY OF ARCHITECTURE. Part I. 100. Arch at Der el Babri. (Lepsius.; the arch was a usual and well-understood building expedient, and one consequently Avhich we may fairly assume to have been long in use. On the other hand, we have in the temple at Der el Bahri in Thebes, built by Thothmes III., a curious example of the retention of the old form, when at first sight it would appear as though the true arcli would have been a more cor- rect expedient. In this example, the lower arch is composed of stones bracketing forward liorizon- tally, though the form of the arch is semicircular ; and above this is a discharging arch of two stones used as in the Pyramids. The upper arch is so arranged as to relieve the crown of the lower — which is its weakest part — of all weight, and at the same time to throw the whole pressure on the outer ends of the arch stones, exactly Avhere it is wanted. The whole thus becomes constructively perfect, though it is a more expensive way of attaining the end desired than by an arch. The truth seems to be, the Egyptians had not at this age invented voussoirs deeper in the direction of the radii of the arch than in that of its perimeter; and the arch Avith them was consequently not generally an appropriate mode of roofing. It was the Romans with their tiles who first really understood the true employment of the arch. So far as we can now understand from the discoveries that have been made, it seems that the Assyrians used the pointed arch for tunnels, aqueducts, and generally for underground work where they feared great superincumbent pressure on the apex, and the round arch above-ground, where that was not to be dreaded; and in this they probably showed more science and discrimination than we do in such works. In Europe the oldest arch is probably that of Cloaca Maxima at Rome, constructed under the early kings. It is of stone, in 3 rims, and shows as perfect a knowledge of the princi])le as any subsequent example. Its lasting uninjured to the pres- ent day ])roves how well the art was then understood, and, by inference, how long it ,„. .,,,,,„ ,, . Tiiust have been practised before reaching 101. Aroh of the Cloaca Maxima, ' ^ Rome. Scale 50 ft. to 1 in. that degree of perfection. From all this it becomes almost certain that the arch was used as
