and deep morasses added to the difficulties of approach. To the
south, however, on the far side of Lake Chalco, lay a more level
tract, but accessible only by roads which the Mexicans deemed
impracticable. Despite the difficulties of the route, the manoeuvre
of Cerro Gordo was repeated on a grander scale.

August 16 to 18.

After a toilsome march of seven-and-twenty miles from Ayotla, over
the spurs of the sierras, the troops reached the great road which
leads to the capital from the south. Across this road was more than
one line of fortifications, to which the Mexican army had been
hurriedly transferred. The hacienda of San Antonio, six miles from
the city, strengthened by field-works and defended by heavy guns,
commanded the highway. To the east was a morass, and beyond the
morass were the blue waters of Lake Chalco; while to the west the
Pedregal, a barren tract of volcanic scoriae, over whose sharp rocks
and deep fissures neither horse nor vehicle could move, flanked the
American line of march. The morass was absolutely impassable.

August 19.

The gloomy solitude of the Pedregal, extending to the mountains, five
miles distant, seemed equally forbidding; but the engineer officers
came once more to the rescue. A road across the Pedregal, little
better than a mule track, was discovered by Captain Lee. Under cover
of a strong escort it was rapidly improved, and Pillow's and Worth's
divisions, accompanied by Magruder's battery, were directed to cross
the waste of rocks. Beyond the Pedregal was a good road, approaching
the city from the south-west; and by this road the post of San