The American army advanced by the way of Ayotla. The route was the
great national road from Vera Cruz to Mexico. The last fifteen miles
of the way was occupied with fortifications, both natural and
artificial, and it seemed impossible to advance directly to the gates
of the city. The army was accordingly brought around Lake Chalco, and
thence westward to San Augustine. This place is ten miles from the
capital. The approach now lay along causeways, across marshes and the
beds of bygone lakes. At the further end of each causeway, the
Mexicans had built massive gates. There were almost inaccessible
positions at Contreras, San Antonio and Molino del Rey. Further on
toward the city lay the powerful bulwarks of Churubusco and
Chapultepec. The latter was of great strength, and seemed impregnable.
These various outposts were held by Santa Anna with a force of fully
thirty thousand Mexicans.

The first assaults of the Americans were made on the nineteenth of
August, by Generals Pillow and Twiggs. The line of communications
between Contreras and Santa Anna's army was cut, and in the darkness
of the following night an assault was made by General Persifer F.
Smith, who about sunrise carried the place and drove the garrison
pell-mell. This was the _first_ victory of the memorable twentieth of
August.

A few hours later, General Worth compelled the evacuation of San
Antonio. This was the _second_ victory. About the same time, General
Pillow advanced on Churubusco, and carried one of the heights. The
position was taken by storm, and the enemy scattered like chaff. This
was the _third_ triumph. The division of General Twiggs added a
_fourth_ victory by storming and holding another height of Churubusco,
while the _fifth_ and last was achieved by General Shields and Pierce,