of course unknown to the Mexicans, who had no beasts of burden.  In the suburbs the natives settled themselves after their own fashion, baking adobes, large mud bricks, in the sun, and building with them one-storey houses with flat roofs, much as they do at the present day.  And thus a new Mexico, nearly the same as that we are now exploring, came to be planted in the midst of the waters.  Three centimes have elapsed since; the city has grown larger, churches, convents, and public buildings have increased, but the architectural character of the place has scarcely altered.  It is the situation that has changed.  The lake of Tezcuco is four miles off, though the causeways which once connected the city with the dry land still exist, and have even been enlarged.  They look like railway-embankments crossing the low ground, and serve as dykes when there is a flood, a casualty which still often happens.

This change is interesting to the student of physical geography; and Humboldt’s account of the causes which have brought it about is full and explicit.  When Mexico had been built a few years, the frightful inundations which threatened its very existence at length awoke the Spaniards to a sense of the mistake that had been made in placing themselves but a few feet above the lowest level of the valley, in such a way that, from whatever point the flood might come, they were sure to get the benefit of it.  The Spanish authorities at home, with their usual sagacity, sent over peremptory orders that the city should be abandoned, and a new capital built at Tacubaya—­a proposal something like intimating to the inhabitants of Naples that their position, at the foot of Mount Vesuvius, was most dangerous, and that they must leave it and settle somewhere else.  In those days the valley was a complete basin, with no outlet—­at least not one worth mentioning; and the heavy tropical rains and the melted snow from the mountains, poured vast quantities of water into it.  Had the valley been at the level of the sea, it would simply have become a great lake, surrounded by hills; but at three thousand feet higher, the atmosphere is rarefied, and evaporation goes on with such rapidity as to keep the accumulation of water in check.  So the affair had adjusted itself in this wise, that the land and the five lakes should divide the valley about equally between them.  It became necessary to alter this state of things, and a passage was cut at a place where the hills were but little above the level of the highest lake.  The history of this passage, the famous “Desague de Huehuetoca,” is instructive enough, but it has been written so threadbare that I cannot touch it.  Suffice it to say, that by this means a constant outlet was made for the lake of Zumpango, the highest of the five, and for the Rio de Guatitlan, a stream which formerly ran into it.