For more than 4000 years before the start of our period, from the first emergence of the Pharaonic kingdom, Egypt had carried the most densely packed and the most easily accessible agricultural population of any part of Africa or, possibly, of the world. This population was concentrated entirely in the Delta and beside the flood plain of the Nile, where the fertility of the soil was maintained by the silt carried down by the river and deposited over the farmlands by the annual flood. The water which carried the precious silt carried also the boats of the corn merchant and the tax gatherer. Every cultivated holding was within sight of the river or the canal bank. Every peasant smallholder could be forced to disgorge his taxes in kind, money and labour. Thus, although the peasants might live very near the subsistence level, suffering severely in the seasons following a poor flood, their combined taxes could support a rich and powerful superstructure of centralised government and military might. It seemed to make little difference to the system whether or not the ruling élite was a foreign one, and in fact since early in the first millennium bc it had always been so. Persians were followed by Greeks, Greeks by Romans, Romans by Byzantines, Byzantines by Arabs, and Arabs by Turks.