The Egyptians, however, left to themselves for a number of centuries, began rapid ascendency. First, as before stated, their food supply was permanent and abundant. Second, there were inducements also for the development of the art of measurement of land which later led to the development of general principles of measurement. There was observation of {158} the sun and moon and the stars, and a development of the art of building of stone and brick, out of which the vast pyramid tombs of kings were built. The artificers, too, had learned to work in precious stones and metals and weave garments, also to write inscriptions on tombs and also on the papyrus. It would seem as if the civilization once started through so many centuries had become sufficiently substantial to remain permanent or to become progressive, but Egypt was subject to a great many drawbacks. The nation that has the food supply of the world is sooner or later bound to come into trouble. So it appears in the case of Egypt, with her vast food resources and accumulation of wealth; she was eventually doomed to the attacks of jealous and envious nations. The history of Egypt is represented by dynasties of kings and changes of government through a long period interrupted by the invasion of tribes from the west and the north, which interfered with the uniformity of development. It is divided into two great centres of development, Lower Egypt, or the Delta, and Upper Egypt, frequently differing widely in the character of civilization. Yet, in the latter part of her supremacy Egypt went to war with the Semitic peoples of Babylon and Assyria for a thousand years. It was the great granary of the world and a centre of wealth and culture.