Crusade, who seized and held the city of Damietta from 1219 to 1221, and again under Louis IX of France, who held it from 1248 to 1249; but in the interval between these two Crusades the Emperor Frederick II was on friendly and even intimate terms with the sultans.[1397] William of Tyre, who knew Egypt at first hand, gives a vivid picture of the fertile strip of country, hemmed in on either side by two deserts “in which the land is so burned and sterile that it supports no herb and no manner of tree, except where the river Nile waters the ground when it is in flood; in these parts alone a great abundance of wheat can grow.”[1398] He speaks of the flood of the Nile, between the months of June and September, and how it leaves a rich deposit of silt; of the palm gardens like a forest along the banks of the stream; and of the extensive orchards of fruit trees in the neighborhood of Alexandria.[1399] He also fully describes the caliph’s palace at Cairo and the Mamelukes, or sultan’s bodyguard, recruited from the children of captured enemies.[1400] Benjamin of Tudela also marveled at the agricultural wealth of the flood plain of the Nile. The river alone, he said, irrigates and fertilizes the land, for “no rain falls, neither is ice or snow ever seen” (Adler’s translation). Among other curiosities he described the Nilometer, which measured the height of the flood waters, and he gave details regarding the agricultural crops and fruits. Benjamin quoted the correct explanation of the flood: “The Egyptians say that up the river, in the land of Al-Habash (Abyssinia), which is the land of Havilah, much rain descends at the time of the rising of the river, and this abundance of rain causes the river to rise and to cover the surface of the land” (Adler’s translation).[1401] AFRICA WEST OF EGYPT