The location and great population of some of their cities required a familiar knowledge of hydraulic operations to supply them with water; and hence it would seem as if they had cultivated this department of the arts equally with others, for some of their Aqueducts were of a character that would have done honor to Greece or Rome. Nearly all the ancient cities of Mexico were supplied by them. “The city of _Mexico_, which was built on several islands near the shore of the lake, was connected to the main land by four great causeways or dikes, the remains of which still exist. One of these to the south, the same by which Cortez entered, was nearly two leagues long--another to the north about one league, and the third at the west somewhat less. The fourth supported the celebrated Aqueduct of Chapoltepec, by which water was conducted from springs, upon an insulated hill of that name, at the distance of from two to three miles.” The Aqueduct of Chapoltepec was the work of Montezuma, and also the vast stone reservoir connected with it. This Aqueduct consisted of two conduits formed of solid mason work--each five feet high and two paces broad--by which the water was introduced into the city for the supply of various fountains. Olid and Alvarado commenced the siege of Mexico by attempting to cut off this supply of water, an enterprise which the Mexicans endeavored to prevent. “There appeared on that side,” says De Solis, “two or three rows of pipes, made of trees hollowed, supported by an Aqueduct of lime and stone, and the enemy had cast up some trenches to cover the avenue to it. But the two captains marched out of Tacuba with most of their troops, and though they met with a very obstinate resistance, they drove the enemy from their post, and broke the pipes and Aqueduct in two or three places, and the water took its natural course into the lake.” Humboldt says, there are still to be perceived the remains of another Aqueduct, which conducted to the city the waters of the spring of Amilco, near Churubusco. This Aqueduct, as described by Cortez, consisted of two conduits composed of clay tempered with mortar, about two paces in breadth, and raised about six feet. In one of them was conveyed a stream of excellent water, as large as the body of a man, into the centre of the city. The other was empty, so that when it became necessary to clean or repair the former, the water might be turned into it; which was the case also with those of Chapoltepec, “of which one was always in use, whenever the other required cleaning.” The gardens of Montezuma were also adorned and nourished with streams and _fountains_, and appear to have rivalled those of Asiatic monarchs in splendour.