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Rh the flank and rear of the assailants whenever they should attack the intrenchments. Till then no conflict was to be engaged in, save to harass the advance. The city itself possessed many natural advantages, which, with means and prudent generalship, might have rendered her wellnigh impregnable. The prevailing rains had transformed the surrounding lands, formerly covered by the now half-drained lake, into a marsh which presented almost insurmountable obstacles, especially on the east side. Approach was therefore confined to the several raised causeways, notably the south-eastern or Vera Cruz road, the southern to Tlalpam and Acapulco, the western to Chapultepec and Toluca, and the northern to Guadalupe. Between these lay a number of minor or branch roads, especially on the south and west, each protected more or less by barricades, lunettes, trous-de-loup, and wet ditches. Beyond rose a line of formidable outworks, centring on the north side upon the hills near Guadalupe, with a score of guns. The hill fortress of Chapultepec, two miles off, commanded the western roads of San Cosme and Belen, and the square-bastioned citadel of the city adjoined the latter gate. The southern approaches were defended by strong works at Churubusco and Mexicalcingo, nearly five miles from the city, and at San Antonio, still farther south; while the eastern were enfiladed by the impregnable rock known as El Peñon, now surrounded by the overflowing waters. The route between the lakes of Chalco and Tezcuco was regarded as the only one practicable for the enemy, and although nature had assisted in protecting the eastern semicircle, the southern and south-eastern outworks received special attention. Between the southern and western points of the exterior line, however, lay a wide, open stretch, and the corresponding inner works were of no importance; but it was supposed that this weak spot could be readily strengthened in case of need.