INUNDATIONS. 315 



northern, is 29-211 inches higher than the surface 

 of Tezcuco ; Avhile that of Chalco, at the southern 

 extremity, is only 3-632 feet more elevated than the 

 great square of Mexico. 



In consequence of this peculiarity, the city has, 

 for a long- series of ages, been exposed to inunda- 

 tions. The lake of Zumpango, swelled by an unusual 

 rise of the Rio de Guautitlan, flows over into that of 

 San Christobal, which again bursts the dike that 

 sep-arates it from Tezcuco. The water of this last 

 is consequently augmented, and flows with impet- 

 uosity into the streets of Mexico. Since the arrival 

 of the Spaniards the town has experienced five 

 great floods, the latest of which happened in 1629. 

 In more recent periods there have been several 

 alarming appearances, but the city was preserved 

 from any actual loss by the desague or canal, w^hich 

 ■was formed for the purpose. 



The situation of the capital is more exposed to 

 danger, because the bed of the lake is progressively 

 rising in consequence of the mud carried into it, and 

 the difference between it and the level of the plain 

 diminishing. Previous to the conquest, and for some 

 time after, it was defended by dikes ; but this method 

 having been found ineff'ectual, the viceroy in 1607 

 employed Enrico Martinez, a native of Germany, to 

 eff"ect the evacuation of the lakes. After making an 

 exact survey of the valley, he presented two plans 

 for canals, the one to empty those of Tezcuco, Zum- 

 pango, and San Christobal, the other to drain that of 

 Zumpango alone. The latter scheme was adopted, 

 and inconsequence, the famous subterraneous gal- 

 lery of Nochistongo was commenced on the 28th 

 November, 1607. Fifteen thousand Indians were 

 employed, and after eleven months of continued la- 

 bour the work was completed. Its length was more 

 than 21,654 feet, its breadth 11-482, and its height 

 13-780. On the opposite side of the hill of Nochis- 

 ton^jo is the liio de Tula, which runs into the Rio de 



