In Chaldaea, at least in certain times and at certain places, construction was more careful. In the ruin known as _Babil_, a ruin that represents one of the principal monuments of ancient Babylon, there is nothing between the bricks but earth that must have been placed there in the condition of mud.[176] These bricks may be detached almost without effort. It is quite otherwise with the two other ruins in the same neighbourhood, called respectively _Kasr_ and _Birs-Nimroud_. Their bricks are held together by an excellent mortar of lime, and cannot be separated without breaking.[177] Elsewhere, at Mugheir for instance, the mortar is composed of lime and ashes.[178] [Illustration: PLATE I. BABYLON FROM AN UNPUBLISHED DRAWING BY FELIX THOMAS.] Finally, the soil of Mesopotamia furnished, and still furnishes, a kind of natural mortar in the bituminous fountains that spring through the soil at more than one point between Mossoul and Bagdad.[179] It is hardly ever used in these days except in boatbuilding, for coating the planks and caulking. In ancient times its employment was very general in the more carefully constructed buildings, and, as it was found neither in Greece nor Syria, it made a great impression upon travellers from those countries. They noted it as one of the characteristics of Chaldaean civilization. In the Biblical account of the Tower of Babel we are told: "They had brick for stone, and slime had they for mortar."[180] Herodotus lays stress upon the same detail in his description of the way in which the walls of Babylon were built: "As they dug the ditches they converted the excavated earth into bricks, and when they had enough, they burnt them in the kiln. Finally, for mortar they used hot bitumen, and at every thirty courses of bricks they put a layer of reeds interlaced."[181]