MEXICAN DEFENCES PLAN OF ATTACK. 409 



These, — together with the strong citadel, lying near the garita 

 of Belen in the south-western corner of the city, — were the prin- 

 cipal external defences still remaining beyond the immediate limits 

 of the capital. The city itself stands on a slight swell between lake 

 Tezcoco and the western edge of the valley, and, throughout its 

 greater extent, is girdled by a ditch or navigable canal extremely 

 difficult to bridge in the face of an enemy, which serves the Mexi- 

 cans not only as a military defence but for drainage and protection 

 of their customs. Each of the eight strong city gates w T ere pro- 

 tected by works of various character and merit. Outside and 

 within the cross fires of these gates there were other obstacles 

 scarcely less formidable towards the south. The main approaches 

 to the city across the flat lands of the basin are raised on causeways 

 flanked by wide and deep ditches designed for their protection and 

 drainage. These causeways, as well as the minor cross roads 

 which are similarly built, were cut in many places and had their 

 bridges destroyed so as to impede the American's advance and to 

 form an entangling net work; while the adjacent meadows were in 

 this rainy season either filled with water in many places or liable to 

 be immediately flooded by a tropical storm. 



With these fields for his theatre of action, and these defences still 

 in front of him, it was an important and responsible question, whether 

 General Scott should attack Mexico on the west or on the south. 



There can be hardly a doubt that the capture of the hill and 

 castle of Chapultepec, before assaulting the city, was imperatively 

 demanded by good generalship. If the capital were taken first, 

 the Mexicans instead of retreating towards Guadalupe and the 

 north, when we attacked and captured from the south, would of 

 course retire to the avoided stronghold of Chapultepec ; and, if our 

 slender forces were subsequently obliged to leave the city in order 

 to take the fortress, our sick, wounded and thinned regiments would 

 be left to the mercy of the mob and the leper os. Chapultepec would 

 thus become the nucleus and garrison of the whole Mexican army, 

 and we might be compelled to fight two battles at the same time, — 

 one in the city, and the other at the castle. But, by capturing the 

 castle first, and seizing the road northward beyond it, we possessed 

 all the most important outworks in the lap of the valley, and cut 

 off the retreat of the Mexicans from the city either to the west, to 

 the castle, or towards our rear in the valley. We obtained, more- 

 over, absolute command of two of the most important entrances to 

 the capital, inasmuch as from the eastern foot of the hill of Cha- 

 pultepec two causeways, and aqueducts raised on lofty arches, di- 



