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. This mound was strengthened by intrenchments at its
base and summit, and rendered a direct attack impracticable.

Scott's army was rapidly concentrated about Ayotla and other points near
the eastern end of Lake Chalco. Reconnoissances were made up to within
gun-shot of El Penon, while engineers were seeking a route by the south
side of Lake Chalco to flank the city, and come upon it from the south
and south-west. A way was found around the lake, and by the 18th of
August troops were in St. Augustin Tlalpam, a town about eleven miles
due south from the plaza of the capital. Between St. Augustin Tlalpam
and the city lie the hacienda of San Antonio and the village of
Churubusco, and south-west of them is Contreras. All these points,
except St. Augustin Tlalpam, were intrenched and strongly garrisoned.
Contreras is situated on the side of a mountain, near its base, where
volcanic rocks are piled in great confusion, reaching nearly to San
Antonio. This made the approach to the city from the south very
difficult.

The brigade to which I was attached--Garland's, of Worth's division--was
sent to confront San Antonio, two or three miles from St. Augustin
Tlalpam, on the road to Churubusco and the City of Mexico. The ground
on which San Antonio stands is completely in the valley, and the surface
of the land is only a little above the level of the lakes, and, except
to the south-west, it was cut up by deep ditches filled with water. To
the south-west is the Pedregal--the volcanic rock before spoken of--over
which cavalry or artillery could not be passed, and infantry would make
but poor progress if confronted by an enemy. From the position occupied
by Garland's brigade, therefore, no movement could be made against the
defences of San Antonio except to the front, and by a narrow causeway,
over perfectly level ground, every inch of which was commanded by the
enemy's artillery and infantry. If Contreras, some three miles west and
south, should fall into our hands, troops from there could move to the
right flank of all the pos