On the plateau beyond this sterile region the Mexicans had gathered in force. Just beyond it General Valencia lay intrenched, with his fine division of about six thousand men and twenty-four guns, commanding the approach from San Augustin. A mile or more north of Contreras lay General Santa Anna, his force holding the main city road.
Such was the situation of the respective armies at the date given, with the Pedregal separating them. Captain Lee, who had already done excellent engineering service at Vera Cruz and Cerro Gordo, assisted by Lieutenants Beauregard and Tower of the engineers, had carefully reconnoitred the position of the enemy, and on the morning of the 19th the advance from San Augustin began, Captain Lee accompanying the troops in their arduous passage across the Pedregal. One of those present thus describes the exploit:
"Late in the morning of the 19th the brigade of which my regiment was a part (Riley's) was sent out from San Augustin in the direction of Contreras. We soon struck a region over which it was said no horses could go, and men only with difficulty. No road was available; my regiment was in advance, my company leading, and its point of direction was a church-spire at or near Contreras. Taking the lead, we soon struck the Pedregal, a field of volcanic rock like boiling scoria suddenly solidified, pathless, precipitous, and generally compelling rapid gait in order to spring from point to point of rock, on which two feet could not rest and which cut through our shoes. A fall on this sharp material would have seriously cut and injured one, whilst the effort to climb some of it cut the hands.
"Just before reaching the main road from Contreras to the city of Mexico we reached a watery ravine, the sides of which were nearly perpendicular, up which I had to be pushed and then to pull others. On looking back over this bed of lava or scoria, I saw the troops, much scattered, picking their way very slowly; while of my own company, some eighty or ninety strong, only five men crossed with me or during some twenty minutes after.
"With these five I examined the country beyond, and struck upon the small guard of a paymaster's park, which, from the character of the country over which we had passed, was deemed perfectly safe from capture. My men gained a paymaster's chest well filled with bags of silver dollars, and the firing and fuss we made both frightened the guard with the belief that the infernals were upon them and made our men hasten to our support.
"Before sundown all of Riley's, and I believe of Cadwallader's, Smith's, and Pierce's brigades, were over, and by nine o' clock a council of war, presided over by Persifer Smith and counselled by Captain R. E. Lee, was held at the church. I have always understood that what was devised and finally determined upon was suggested by Captain Lee; at all events, the council was closed by his saying that he desired to return to General Scott with the decision of General Smith, and that, as it was late, the decision must be given as soon as possible, since General Scott wished him to return in time to give directions for co-operation.
"During the council, and for hours after, the rain fell in torrents, whilst the darkness was so intense that one could move only by groping. To illustrate: my company again led the way to gain the Mexican rear, and when, after two hours of motion, light broke sufficiently to enable us to see a companion a few feet off, we had not moved four hundred yards, and the only persons present were half a dozen officers and one guide."
Much is said of the perils of war and of the courage necessary to face them. But who would not rather face a firing-line of infantry in full daylight than to venture alone in such a dark and stormy night as was this upon such a perilous and threatening region as the Pedregal, in which a misstep in the darkness would surely lead to wounds and perhaps to death. Its crossing, under such conditions, might well be deemed impossible, had not Captain Lee succeeded, borne up by his strong sense of duty, in this daring enterprise.
General Scott, who was very anxious to know the position of the advance forces, had sent out seven officers about sundown with instructions to the troops at Contreras, but they had all returned, completely baffled by the insuperable difficulties of the way. Not a man except Robert E. Lee had the daring, skill, and persistence to cross this region of volcanic knife-blades on that night of rain and gloom.
The writer above quoted from says, "History gives him the credit of having succeeded, but it has always seemed incredible to me when I recollect the distance amid darkness and storm, and the dangers of the Pedregal which he must have traversed. Scarcely a step could be taken without danger of death; but that to him, a true soldier, was the willing risk of duty in a good cause."