Along the Chalco route there were no more fortifications, but west of lakes Chalco and Xochimilco, a line of entrenchments had been commenced, connecting the fortified hacienda, or massive stone plantation house of San Antonio, about six miles south of the city, with the town of Mexicalzingo. West of this hacienda, the Pedregal, a vast, broken field of lava, spread out along the edge of the main road, and skirting it to San Agustin, extended high upon the mountain slopes still further west near San Angel and Contreras, whose neighboring fields were cut into deep ravines and barrancas by the wash from the declivities. The Pedregal was a most formidable obstacle in the march or manœuvres of an army. But few levels of arable land were found among its rocky wastes. It admitted the passage of troops at but few points, and was entirely impracticable for cavalry or artillery, except by a single mule-path. [70] North of San Angel and the edge of the Pedregal, at the distance of about four miles, rose the solitary hill and castle of Chapultepec, which had been amply prepared for defence; and still further north on the same line, frowned the stern ridges of the sierra, cut by barrancas and profound dells, until the ring of the outer series of military works was thus finally united at the pass beyond Tenepantla. But inside of this formidable barrier of outworks, nearer the city, another line of fortifications had been prepared to dispute the American march. The first, and perhaps the most important of these, was at Churubusco, a scattered village lying midway between San Agustin and the city of Mexico, directly on the road, at a spot where the stream or rivulet of Churubusco runs eastwardly from a point on the road from San Angel to the capital, towards the lake of Xochimilco. The sides of the water course were planted with the prickly maguey, and one of the most western buildings in the village was a strong massive stone convent, whose walls had been cut for musketry, and whose parapets, azotéas or flat roofs, and windows, all afforded suitable positions for soldiery. Large quantities of ammunition were stored within the edifice. The enclosure of the church and convent was defended by about two thousand men, and mounted seven guns, while, towards the east was a beautiful, solid and scientifically constructed tête de pont which covered the bridge over the stream by which the road led to the capital. In this work three heavy guns were mounted, while the neighborhood is said to have swarmed with troops.
We have already mentioned the garita or gate of San Lazaro, which was the entrance to the city by the main road from the east, passing the hill and fortification of El Peñon. This garita was strengthened by strong works on the road, with platforms and embrasures for heavy cannon, which would have swept the path, while the marshes on the south were protected by redoubts and lunettes extending to the garita or entrance of La Candelaria on the canal from Xochimilco. North of San Lazaro strong works hemmed in the city to the garita of Peralvillo, and connected with defences and fortified houses reaching to the garita of Santiago. Other advanced works were begun in that quarter, while the ground in front of the main line was cut into troux de loups.
On the west of the city are the garitas of San Cosmé and Belen. "Works had been commenced to connect that of San Cosmé, the most northerly of the two, with that of Santiago, and the nature of the country and of the buildings, formed obstructions to any advance between San Cosmé and Belen. Belen was defended principally by the citadel of Mexico, a square bastioned work with wet ditches, immediately inside the garita. Barricades had also been commenced; but the great obstacle to an entrance by either garita, was presented in the rock and castle of Chapultepec, two miles south-west of the city. From this hill two aqueducts extend to the capital, the one, north-east, in a direct line to Belen, and the other, north, to the suburb of San Cosmé, where, turning at right angles, it continued onward and entered at the garita. The roads from the west ran along the sides of the aqueducts. Two roads enter the city from the south, between the garita of San Antonio and Belen, one at Belen and the other at the garita of El niño Perdido, neither of these roads have branches to the Acapulco road south of the Pedregal and the Hacienda of San Antonio, and, therefore, had been left comparatively unfortified." [71]
These defences, overlooked by the lofty sierras and the barrancas which broke their feet, hemmed in the capital, and the Mexicans readily imagined that they could not be turned by an army marching from the east, so as to reach the city on the west, except by a tedious circuit which would allow them time to complete their protective works in that quarter. The east had claimed their chief and most natural attention, and thus the south and the west became unquestionably their weakest points.
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Such were the Mexican lines, natural and artificial, around the capital in the valley in the middle of August, 1847, and such was the position of the American troops in front of them. The Mexicans numbered then, with all their levies, probably more than thirty thousand fighting men, while the Americans did not count more than ten thousand—under arms at all points. The invaders had prepared as well as circumstances admitted, and their materiel for assault or siege had been gathered carefully, and transported slowly into the interior, through the country intervening between Vera Cruz and Puebla, every train being usually attacked by guerillas, and fighting its way boldly through the most dangerous passes.
The equipments of the Mexicans, except the weapons saved from the wreck of former battles, had been chiefly prepared at the cannon foundries and powder factories of the country, and it is quite amazing to notice how completely a great exigency brought forth the latent energies of the people, teaching them what they might ordinarily effect, if guided by a spirit of industry and progress. Under the most disheartening depression, but fired by the stimulus of despair, by an overpowering sense of patriotic duty, and by religious enthusiasm which had been excited by the crusading address of the clergy of San Luis Potosi, issued in the month of April, they manifested in their last moments, a degree of zeal, calmness, and foresight that will forever redound to their credit on the page of history.
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The Mexican preparations for defence were not, of course, as completely known to the Americans as we now describe them. Through spies, scouts and reconnoisances of our engineers, some of the exterior, and even of the interior lines were ascertained with tolerable accuracy; but sufficient was known to satisfy General Scott that of all the approaching routes to the capital, that which led along the southern shores of lake Chalco was the only one he ought to adopt. [72]
Accordingly, on the 15th of August, the movement was commenced in the reverse order from that in which the army had entered the valley from Puebla. Worth's division passing Pillow's, led the advance, Pillow and Quitman followed, while Twiggs' brought up the rear. Scott took his position with Pillow, so as to communicate easily with all parts of the army. Water transportation, to some extent, had been obtained by General Worth at Chalco, by the siezure of market boats which plied between that place and the capital. When Twiggs moved he was assailed by Alvarez and his Pintos, but soon drove them off, while the advance columns, after passing San Gregorio, were frequently assailed by the enemy's light troops in their front, and harassed and impeded by ditches that had been hastily cut across the road, or by rocks rolled down from the mountains. These obstacles necessarily consumed time, but the simple-minded Indians of the neighborhood, who had just been compelled by the Mexicans to throw the impediments in the Americans' way, were perhaps more easily induced to aid in clearing the path for the invaders, than their ancestors had been in the days of Cortéz. On the afternoon of the 17th, Worth, with the advance, reached San Agustin, at the foot of the mountains, and at the intersection of the southern road from Mexico to Cuernavaca and Acapulco—a point whose topography we have already described;—and, on the 18th, the rear division entered the town.