364 WORKS UNDERTAKEN FOR _ 
ger, because the bed of the lake is progressively ris- 
ing in consequence of the mud carried into it, and the 
difference between it and the level of the plain di- 
minishing. Previous to the conquest, and for some 
time after, it was defended by dikes ; but this me- 
thod having been found ineffectual, the viceroy in 
1607 employed Enrico Martinez, a native of Ger- 
many, to effect 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 Tez- 
cuco, Zumpango, and San Christobal, the other to 
drain that of Zumpango alone. The latter scheme 
was adopted, and in consequence, the famous sub- 
terraneous gallery of Nochistongo was commenced 
on the 28th November 1607. Fifteen thousand In- 
dians were employed, and after eleven months of 
continued labour 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 Nochistongo is the Rio de Tula, 
which runs into the Rio de Panuco, and from 
the northern or further extremity of the gallery 
an open trench, 28,216 feet long, was cut to carry 
the water to the former river. Soon after the cur- 
rent began to flow through this artificial channel, 
it gradually occasioned depositions and erosions, so 
that it became necessary to support the roof, which 
was composed of marl and clay. For this purpose 
wood was at first employed, and afterwards masonry ; 
but the arches being soon undermined, the passage 
at length was obstructed. 
Several plans were now proposed, and in 1614 
the court of Madrid sent to Mexico a Dutch engi- 
neer, Adrian Boot, who advised the construction of 
