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.