highest level in May; before the end of June it again subsides.  More sluggish in movement, the Euphrates, which is 1780 miles long, shows signs of rising a fortnight later than the Tigris, and is in flood for a more extended period; it does not shrink to its lowest level until early in September.  By controlling the flow of these mighty rivers, preventing disastrous floods, and storing and distributing surplus water, the ancient Babylonians developed to the full the natural resources of their country, and made it—­what it may once again become—­one of the fairest and most habitable areas in the world.  Nature conferred upon them bountiful rewards for their labour; trade and industries flourished, and the cities increased in splendour and strength.  Then as now the heat was great during the long summer, but remarkably dry and unvarying, while the air was ever wonderfully transparent under cloudless skies of vivid blue.  The nights were cool and of great beauty, whether in brilliant moonlight or when ponds and canals were jewelled by the lustrous displays of clear and numerous stars which glorified that homeland of the earliest astronomers.

Babylonia is a treeless country, and timber had to be imported from the earliest times.  The date palm was probably introduced by man, as were certainly the vine and the fig tree, which were widely cultivated, especially in the north.  Stone, suitable for building, was very scarce, and limestone, alabaster, marble, and basalt had to be taken from northern Mesopotamia, where the mountains also yield copper and lead and iron.  Except Eridu, where ancient workers quarried sandstone from its sea-shaped ridge, all the cities were built of brick, an excellent clay being found in abundance.  When brick walls were cemented with bitumen they were given great stability.  This resinous substance is found in the north and south.  It bubbles up through crevices of rocks on river banks and forms small ponds.  Two famous springs at modern Hit, on the Euphrates, have been drawn upon from time immemorial.  “From one”, writes a traveller, “flows hot water black with bitumen, while the other discharges intermittently bitumen, or, after a rainstorm, bitumen and cold water....  Where rocks crop out in the plain above Hit, they are full of seams of bitumen."[30] Present-day Arabs call it “kiyara”, and export it for coating boats and roofs; they also use it as an antiseptic, and apply it to cure the skin diseases from which camels suffer.

Sumeria had many surplus products, including corn and figs, pottery, fine wool and woven garments, to offer in exchange for what it most required from other countries.  It must, therefore, have had a brisk and flourishing foreign trade at an exceedingly remote period.  No doubt numerous alien merchants were attracted to its cities, and it may be that they induced or encouraged Semitic and other raiders to overthrow governments and form military aristocracies, so that they themselves might obtain necessary concessions