The ice in the Delaware impeded the crossing of the American troops, and gave the British time to draw in their scattered cantonments and assemble their whole force at Princeton. Information was obtained that Lord Cornwallis had joined General Grant with a reinforcement of chosen troops. They had now seven or eight thousand men, and were pressing wagons for a march upon Trenton. Word, too, was brought that General Howe was on the march with a thousand light troops, with which he had landed at Amboy.
The situation of Washington was growing critical. The enemy were beginning to advance their large pickets towards Trenton. Everything indicated an approaching attack. The force with him was small; to retreat across the river would destroy the dawn of hope awakened in the bosoms of the Jersey militia by the late exploit, but to make a stand without reinforcements was impossible. In this emergency he called to his aid General Cadwalader from Crosswicks, and General Mifflin from Bordentown, with their collective forces amounting to about three thousand six hundred men. They promptly answered to his call, and marching in the night, joined him on the 1st of January.
Washington chose a position for his main body on the east side of the Assunpink. There was a narrow stone bridge across it, where the water was very deep; the same bridge over which part of Rahl's brigade had escaped in the recent affair. He planted his artillery so as to command the bridge and the fords. His advance guard was stationed about three miles off in a wood, having in front a stream called Shabbakong Creek. Early on the morning of the 2d, came certain word that Cornwallis was approaching with all his force. Strong parties were sent out under General Greene, who skirmished with the enemy and harassed them in their advance. By twelve o'clock they reached Shabbakong, and halted for a time on its northern bank. Then crossing it, and moving forward with rapidity, they drove the advance guard out of the woods, and pushed on until they reached a high ground near the town. Here Hand's corps of several battalions was drawn up and held them for a time in check. All the parties in advance ultimately retreated to the main body, on the east side of the Assunpink.
From all these checks and delays it was nearly sunset before Cornwallis, with the head of his army, entered Trenton. His rear-guard under General Leslie rested at Maiden Head, about six miles distant, and nearly half way between Trenton and Princeton. Forming his troops into columns, he now made repeated attempts to cross the Assunpink at the bridge and the fords, but was as often repulsed by the artillery. For a part of the time Washington, mounted on a white horse, stationed himself at the south end of the bridge, issuing his orders. Each time the enemy was repulsed there was a shout along the American lines. At length they drew off, came to a halt, and lighted their camp fires. The Americans did the same, using the neighboring fences for the purpose.
A cannonade was kept up on both sides until dark; but with little damage to the Americans. When night closed in, the two camps lay in sight of each other's fires, ruminating the bloody action of the following day. It was the most gloomy and anxious night that had yet closed in on the American army throughout its series of perils and disasters; for there was no concealing the impending danger. But what must have been the feelings of the commander-in-chief as he anxiously patrolled his camp and considered his desperate position? A small stream, fordable in several places, was all that separated his raw, inexperienced army from an enemy vastly superior in numbers and discipline, and stung to action by the mortification of a late defeat. In this darkest of moments a gleam of hope flashed upon his mind: a bold expedient suggested itself. Almost the whole of the enemy's force must by this time be drawn out of Princeton and advancing by detachments toward Trenton, while their baggage and principal stores must remain weakly guarded at Brunswick. Was it not possible by a rapid night-march along the Quaker road, a different road from that on which General Leslie with the rear-guard was resting, to get past that force undiscovered, come by surprise upon those left at Princeton, capture or destroy what stores were left there, and then push on to Brunswick? This would save the army from being cut off; would avoid the appearance of a defeat; and might draw the enemy away from Trenton, while some fortunate stroke might give additional reputation to the American arms.
Such was the plan which Washington revolved in his mind on the gloomy banks of the Assunpink, and which he laid before his officers in a council of war, held after nightfall, at the quarters of General Mercer. It met with instant concurrence. One formidable difficulty presented itself. The weather was unusually mild; there was a thaw, by which the roads might be rendered deep and miry, and almost impassable. Fortunately, the wind veered to the north in the course of the evening; the weather became intensely cold, and in two hours the roads were once more hard and frost-bound. In the meantime, the baggage of the army was silently removed to Burlington, and every other preparation was made for a rapid march. To deceive the enemy, men were employed to dig trenches near the bridge within hearing of the British sentries, with orders to continue noisily at work until daybreak; others were to go the rounds, relieve guards at the bridge and fords, keep up the camp fires, and maintain all the appearance of a regular encampment. At daybreak they were to hasten after the army.
In the dead of the night the army drew quietly out of the encampment and began its march. General Mercer was in the advance with the remnant of his flying camp, now but about three hundred and fifty men. The Quaker road was a complete roundabout, joining the main road about two miles from Princeton, where Washington expected to arrive before daybreak. The road, however, was new and rugged; cut through woods, where the stumps of trees broke the wheels of some of the baggage trains and retarded the march of the troops; so that it was near sunrise of a bright, frosty morning when Washington reached the bridge over Stony Brook, about three miles from Princeton. After crossing the bridge he led his troops along the bank of the brook to the edge of a wood, where a by-road led off on the right through low grounds, and was said by the guides to be a short cut to Princeton and less exposed to view. By this road Washington defiled with the main body, ordering Mercer to continue along the brook with his brigade until he should arrive at the main road, where he was to secure, and if possible destroy a bridge over which it passes, so as to intercept any fugitives from Princeton, and check any retrograde movements of the British troops which might have advanced towards Trenton.
Hitherto the movements of the Americans had been undiscovered by the enemy. Three regiments of the latter, the 17th, 40th, and 55th, with three troops of dragoons, had been quartered all night in Princeton, under marching orders to join Lord Cornwallis in the morning. The 17th regiment, under Colonel Mawhood, was already on the march; the 55th regiment was preparing to follow. Mawhood had crossed the bridge by which the old or main road to Trenton passes over Stony Brook, and was proceeding through a wood beyond when, as he attained the summit of a hill about sunrise, the glittering of arms betrayed to him the movement of Mercer's troops to the left, who were filing along the Quaker road to secure the bridge, as they had been ordered. The woods prevented him from seeing their number. He supposed them to be some broken portion of the American army flying before Lord Cornwallis. With this idea, he faced about and made a retrograde movement to intercept them or hold them in check; while messengers spurred off at all speed to hasten forward the regiments still lingering at Princeton, so as completely to surround them.
The woods concealed him until he had recrossed the bridge of Stony Brook, when he came in full sight of the van of Mercer's brigade. Both parties pushed to get possession of a rising ground on the right near the house of a Mr. Clark. The Americans being nearest, reached it first, and formed behind a hedge fence which extended along a slope in front of the house; whence, being chiefly armed with rifles, they opened a destructive fire. It was returned with great spirit by the enemy. At the first discharge Mercer was dismounted. One of his colonels, also, was mortally wounded and carried to the rear. Availing themselves of the confusion thus occasioned, the British charged with the bayonet; the American riflemen having no weapon of the kind were thrown into disorder and retreated. Mercer, who was on foot, endeavored to rally them, when a blow from the butt end of a musket felled him to the ground. He rose and defended himself with his sword, but was surrounded, bayoneted repeatedly, and left for dead. Mawhood pursued the broken and retreating troops to the brow of the rising ground, on which Clark's house was situated, when he beheld a large force emerging from a wood and advancing to the rescue. It was a body of Pennsylvania militia, which Washington, on hearing the firing, had detached to the support of Mercer. Mawhood instantly ceased pursuit, drew up his artillery, and by a heavy discharge brought the militia to a stand.
At this moment Washington himself arrived at the scene of action, having galloped from the by-road in advance of his troops. From a rising ground he beheld Mercer's troops retreating in confusion, and the detachment of militia checked by Mawhood's artillery. Everything was at peril. Putting spurs to his horse he dashed past the hesitating militia, waving his hat and cheering them on. His commanding figure and white horse made him a conspicuous object for the enemy's marksmen; but he heeded it not. Galloping forward under the fire of Mawhood's battery, he called upon Mercer's broken brigade. The Pennsylvanians rallied at the sound of his voice, and caught fire from his example. At the same time the 7th Virginia regiment emerged from the wood, and moved forward with loud cheers, while a fire of grapeshot was opened by Captain Moulder of the American artillery from the brow of a ridge to the south.