The densest and most solid of them, he says, instead of yielding with age and sinking under the weight they have to support, take a gentle upward curve so as to become better fitted than at first for the support of the heavy roof.[214] The necessity for the presence of a thick roof between the sun and the inside of the rooms is here very clearly affirmed. It will also be noticed that the general form of apartments in Susiana and Assyria did not escape the observer in question. As he saw very clearly, the great disproportion between their length and their width was to be explained as easily by the requirements of a wooden roof as by those of a clay vault. In his attempt to describe Babylon, Strabo says[215]: "In the absence of timber, properly speaking, beams and columns of palm-wood were used in the buildings of Babylonia. These pillars were covered with twisted ropes of rushes, over which several coats of paint were laid. The doors were coated with asphalte. Both doors and houses were very high. We may add that the houses were vaulted, in consequence of the absence of wood.... There were, of course, no tile roofs in countries where it never rains,[216] such as Babylonia, Susiana and Sittacenia." Strabo himself never visited Mesopotamia. This we know from the passage in his introduction, in which he tells us exactly how far his voyages extended, from north to south, and from east to west.[217] When he had to describe Asia from the Taurus to India, he could only do so with the help of passages borrowed from various authors, and in the course of his work it has sometimes happened that he has brought into juxtaposition pieces of information that contradict each other.[218] Something of the kind has happened in the lines we have quoted, in which he first speaks of pillars and timber roofs, and ends by declaring that all the Chaldaean houses were vaulted, although vaults and timber could not exist together. The truth is, in all probability, that one system of covering prevailed here and another there, and that the seeming contradiction in the text is due to hasty editing. We may conclude from it that travellers had reported the existence of both systems, and that each was to be explained by local conditions and the varying supply of materials.