The inhabitants were therefore, necessarily, agriculturists. They were also irrigators and engineers, compelled to study how best to regulate the supply of water, to turn the pestiferous marsh into a fruitful field, and to confine the rivers and canals within their channels. Agriculture and engineering thus had their natural home in Babylonia, and originated in the character of the country itself. The neighborhood of the sea and the two great waterways which flanked the Babylonian plain further gave an impetus to trade. The one opened the road to the spice-bearing coasts of Southern Arabia and the more distant shores of Egypt; the other led to the highlands of Western Asia. From the first the Babylonians were merchants and sailors as well as agriculturists. The “cry” of the Chaldeans was “in their ships.” The seaport of Eridu was one of the earliest of Babylonian cities; and a special form of boat took its name from the more inland town of Ur. While the population of the country devoted itself to agriculture, the towns grew wealthy by the help of trade. Their architecture was dependent on the nature of the country. In the alluvial plain no stone was procurable; clay, on the other hand, was everywhere. All buildings, accordingly, were constructed of clay bricks, baked in the sun, and bonded together with cement of the same material; their roofs were of wood, supported, not unfrequently, by the stems of the palm. The palm stems, in time, became pillars, and Babylonia was thus the birthplace of columnar architecture. It was also the birthplace of decorated walls. It was needful to cover the sun-dried bricks with plaster, for the sake both of their preservation and of appearance. This was the origin of the stucco with which the walls were overlaid, and which came in time to be ornamented with painting. Ezekiel refers to the figures, portrayed in vermilion, which adorned the walls of the houses of the rich. The want of stone and the abundance of clay had another and unique influence upon Babylonian culture. It led to the invention of the written clay tablet, which has had such momentous results for the civilization of the whole Eastern world. The pictures with which Babylonian writing began were soon discarded for the conventional forms, which could so easily be impressed by the stylus upon the soft clay. It is probable that the use of the clay as a writing material was first suggested by the need there was in matters of business that the contracting parties should record their names. The absence of stone made every pebble valuable, and pebbles were accordingly cut into cylindrical forms and engraved with signs. When the cylinder was rolled over a lump of wet clay, its impress remained forever. The signs became cuneiform characters, and the Babylonian wrote them upon clay instead of stone.