The canals, through which the overflowing waters of the Nile were carried to the more distant fields, were, of course, each year more or less blocked up by the same mud which made the fields fruitful; and the clearing of these canals was one of the greatest boons that the monarch could bestow upon the tillers of the soil. This had often been neglected by the less powerful and less prudent kings of Egypt, in whose reigns the husbandman believed that Heaven in its displeasure withheld part of the wished-for overflow; but Petronius employed the leisure of his soldiers on this wise and benevolent work. In order better to understand the rise of the Nile, to fix the amount of the land-tax, and more fairly to regulate the overflow through the canals, the Nilometer on the Island of Elephantine was at this time made. [Illustration: 011.jpg THE NILOMETER AT ELEPHANTINE] It was under AElius Gallus, the third prefect, that Egypt was visited by Strabo, the most careful and judicious of all the ancient travellers. He had come to study mathematics, astronomy, and geography in the museum, under the successors of Euclid, Eratosthenes, and Hipparchus. He accompanied the prefect in a march to Syene (Aswan), the border town, and he has left us a valuable account of the state of the country at that time. Alexandria was the chief object that engaged his attention. Its two harbours held more ships than were to be seen in any other port in the world, and its export trade was thought greater than that of all Italy. The docks on each side of the causeway, and the ship canal, from the harbour of Eunostus to the Mareotic Lake, were full of bustle and activity. The palace or citadel on the promontory of Lochias on one side of the great harbour was as striking an object as the lighthouse on the other. The temples and palaces covered a space of ground equal to more than one-fourth part of the city, and the suburbs reached even beyond the Mareotic Lake. Among the chief buildings were the Soma, which held the bodies of Alexander and of the Ptolemies; the court of justice; the museum of philosophy, which had been rebuilt since the burning by Caesar's soldiers; the exchange, crowded with merchants, the temple of Neptune, and Mark Antony's fortress, called the Timonium, on a point of land which jutted into the harbour; the Caesarium, or new palace; and the great temple of Serapis, which was on the western side of the city, and was the largest and most ornamented of all these buildings. Farther off was the beautiful gymnasium for wrestlers and boxers, with its porticoes of a stadium in length, where the citizens used to meet in public assembly. From the top of the temple of Pan, which rose like a sugar-loaf in the middle of the city, and was mounted by a winding staircase, the whole of this remarkable capital might be seen spread out before the eye. On the east of the city was the circus, for chariot races, and on the west lay the public gardens and pale green