When Alexander arrived, and perceived the advantages of the situation, he determined to build the city on the (natural) harbour. The prosperity of the place, which ensued, was intimated, it is said, by a presage which occurred while the plan of the city was tracing. The architects were engaged in marking out the line of the wall with chalk, and had consumed it all, when the king arrived; upon which the dispensers of flour supplied the workmen with a part of the flour, which was provided for their own use; and this substance was used in tracing the greater part of the divisions of the streets. This, they said, was a good omen for the city. 7. The advantages of the city are of various kinds. The site is washed by two seas; on the north, by what is called the Egyptian Sea, and on the south, by the sea of the lake Mareia, which is also called Mareotis. This lake is filled by many canals from the Nile, both by those above and those at the sides, through which a greater quantity of merchandise is imported than by those communicating with the sea. Hence the harbour on the lake is richer than the maritime harbour. The exports by sea from Alexandreia exceed the imports. This any person may ascertain, either at Alexandreia or Dicæarchia, by watching the arrival and departure of the merchant vessels, and observing how much heavier or lighter their cargoes are when they depart or when they return. In addition to the wealth derived from merchandise landed at the harbours on each side, on the sea and on the lake, its fine air is worthy of remark: this results from the city being on two sides surrounded by water, and from the favourable effects of the rise of the Nile. For other cities, situated near lakes, have, during the heats of summer, a heavy and suffocating atmosphere, and lakes at their margins become swampy by the evaporation occasioned by the sun’s heat. When a large quantity of moisture is exhaled from swamps, a noxious vapour rises, and is the cause of pestilential disorders. But at Alexandreia, at the beginning of summer, the Nile, being full, fills the lake also, and leaves no marshy matter which is likely to occasion malignant exhalations. At the same period, the Etesian winds blow from the north, over a large expanse of sea, and the Alexandrines in consequence pass their summer very pleasantly.