They do not use tiles for their houses, because there are no great rains. The case is the same in Susiana and in Sitacene. 6. In Babylon a residence was set apart for the native philosophers called Chaldæans, who are chiefly devoted to the study of astronomy. Some, who are not approved of by the rest, profess to understand genethlialogy, or the casting of nativities. There is also a tribe of Chaldæans, who inhabit a district of Babylonia, in the neighbourhood of the Arabians, and of the sea called the Persian Sea.[493] There are several classes of the Chaldæan astronomers. Some have the name of Orcheni, some Borsippeni, and many others, as if divided into sects, who disseminate different tenets on the same subjects. The mathematicians make mention of some individuals among them, as Cidenas, Naburianus, and Sudinus. Seleucus also of Seleuceia is a Chaldæan, and many other remarkable men. 7. Borsippa is a city sacred to Diana and Apollo. Here is a large linen manufactory. Bats of much larger size than those in other parts abound in it. They are caught and salted for food. 8. The country of the Babylonians is surrounded on the east by the Susans, Elymæi, and Parætaceni; on the south by the Persian Gulf, and the Chaldæans as far as the Arabian Meseni; on the west by the Arabian Scenitæ as far as Adiabene and Gordyæa; on the north by the Armenians and Medes as far as the Zagrus, and the nations about that river. 9. The country is intersected by many rivers, the largest of which are the Euphrates and the Tigris: next to the Indian rivers, the rivers in the southern parts of Asia are said to hold the second place. The Tigris is navigable upwards from its mouth to Opis,[494] and to the present Seleuceia. Opis is a village and a mart for the surrounding places. The Euphrates also is navigable up to Babylon, a distance of more than 3000 stadia. The Persians, through fear of incursions from without, and for the purpose of preventing vessels from ascending these rivers, constructed artificial cataracts. Alexander, on arriving there, destroyed as many of them as he could, those particularly [on the Tigris from the sea] to Opis. But he bestowed great care upon the canals; for the Euphrates, at the commencement of summer, overflows. It begins fill in the spring, when the snow in Armenia melts: the ploughed land, therefore, would be covered with water and be submerged, unless the overflow of the superabundant water were diverted by trenches and canals, as in Egypt the water of the Nile is diverted. Hence the origin of canals. Great labour is requisite for their maintenance, for the soil is deep, soft, and yielding, so that it would easily be swept away by the stream; the fields would be laid bare, the canals filled, and the accumulation of mud would soon obstruct their mouths. Then, again, the excess of water discharging itself into the plains near the sea forms lakes, and marshes, and reed-grounds, supplying the reeds with which all