and the first steeps of the mountains forming the southern rim of the valley, until it fell at right angles, at Tlalpam or San Agustin de las Cuevas, into the main road from the city of Mexico towards the southern States of the Republic.
All these routes were boldly reconnoitred by the brave engineers accompanying the American army, and, where they could not extend their personal observations, the officers obtained from the people of the country, information upon which subsequent events proved that they were justified in relying. From the knowledge thus gained as to the route south of the lake of Chalco, they were induced to believe, although it was rough, untravelled, difficult, and narrowly hemmed in between the lake and the mountains, yet that the long and narrow defile, which was open to resistance at many points, was not sufficiently obstructed or fortified to prevent our passage. All the routes on the lower lands, it should also be remembered, were liable to increased difficulties from the deluging rains prevailing at this season on the highlands of Mexico, and which sometimes convert the highways and their borders, for many leagues, into almost impassable lagunes.