CHAPTER XI.
ADVANCE ON THE CITY OF MEXICO--BATTLE OF CONTRERAS--ASSAULT AT CHURUBUSCO--NEGOTIATIONS FOR PEACE--BATTLE OF MOLINO DEL REY--STORMING OF CHAPULTEPEC--SAN COSME--EVACUATION OF THE CITY--HALLS OF THE MONTEZUMAS.
The route followed by the army from Puebla to the City of Mexico was over Rio Frio mountain, the road leading over which, at the highest point, is about eleven thousand feet above tide water.

The pass through this mountain might have been easily defended, but it was not; and the advanced division reached the summit in three days after leaving Puebla.
The City of Mexico lies west of Rio Frio mountain, on a plain backed by another mountain six miles farther west, with others still nearer on the north and south.

Between the western base of Rio Frio and the City of Mexico there are three lakes, Chalco and Xochimilco on the left and Texcoco on the right, extending to the east end of the City of Mexico.
Chalco and Texcoco are divided by a narrow strip of land over which the direct road to the city runs.

Xochimilco is also to the left of the road, but at a considerable distance south of it, and is connected with Lake Chalco by a narrow channel.

There is a high rocky mound, called El Penon, on the right of the road, springing up from the low flat ground dividing the lakes.