The ancient city of Mexico covered the same spot occupied by the modern capital. The great causeways touched it in the same points; the streets ran in much the same direction, nearly from north to south and from east to west; the cathedral in the _plaza mayor_ stands on the same ground that was covered by the temple of the Aztec war-god; and the four principal quarters of the town are still known among the Indians by their ancient names. Yet an Aztec of the days of Montezuma, could he behold the modern metropolis, which has risen with such phœnix-like splendor from the ashes of the old, would not recognize its site as that of his own Tenochtitlan. For the latter was encompassed by the salt floods of Tezcuco, which flowed in ample canals through every part of the city: while the Mexico of our day stands high and dry on the main land, nearly a league distant, at its centre, from the water. The cause of this apparent change in its position is the diminution of the lake, which, from the rapidity of evaporation in these elevated regions, had become perceptible before the Conquest, but which has since been greatly accelerated by artificial causes.[306] The average level of the Tezcucan lake, at the present day, is but four feet lower than the great square of Mexico.[307] It is considerably lower than the other great basins of water which are found in the Valley. In the heavy swell sometimes caused by long and excessive rains, these latter reservoirs anciently overflowed into the Tezcuco, which, rising with the accumulated volume of waters, burst through the dikes, and, pouring into the streets of the capital, buried the lower part of the buildings under a deluge. This was comparatively a light evil when the houses stood on piles so elevated that boats might pass under them; when the streets were canals, and the ordinary mode of communication was by water. But it became more disastrous as these canals, filled up with the rubbish of the ruined Indian city, were supplanted by streets of solid earth, and the foundations of the capital were gradually reclaimed from the watery element. To obviate this alarming evil, the famous drain of Huehuetoca was opened, at an enormous cost, in the beginning of the seventeenth century, and Mexico, after repeated inundations, has been at length placed above the reach of the flood.[308] But what was gained to the useful, in this case, as in some others, has been purchased at the expense of the beautiful. By this shrinking of the waters, the bright towns and hamlets once washed by them have been removed some miles into the interior, while a barren strip of land, ghastly from the incrustation of salts formed on the surface, has taken the place of the glowing vegetation which once enamelled the borders of the lake, and of the dark groves of oak, cedar, and sycamore which threw their broad shadows over its bosom.