After the light infantry fled across the North Bridge, Major Buttrick led his some of his minutemen over the bridge. The minutemen took positions behind a stone wall on a small hill near the bridge. This put the minutemen in strong defensive position from which they could control the North Bridge. The minutemen watched as two companies of grenadiers under command of Colonel Smith came up the road from Concord and halted the retreat of the light infantry after their earlier request for assistance. Smith and his officers reformed the regulars, barely 250 yards from the minutemen but well out of musket range. This left the other four light infantry companies that had been searching Colonel Barrett's farm on the far side of the river, with more than 500 provincial soldiers between them and the main body of regulars in Concord.

When these four companies approached the North Bridge, they found that the three companies left there to guard the bridge for their return were nowhere to be seen. The provincial militia had moved much closer to the bridge, and the regulars could also see that some of the provincials had crossed the bridge and taken a strong position on the Concord side. The regulars probably did not know that there had been shooting at the bridge as they approached, but it was clear that their situation was perilous. The light infantry came down to the bridge and crossed at a quick march. Their path took them close to Colonel Barrett's militia on the west side of the river, and Major Buttrick's minutemen on the Concord side of the river. At this point in the day, however, the Massachusetts men still hesitated to fire on the King's troops, and the light infantry joined the other regulars in the center of Concord without further shooting. In their haste to pass the provincial soldiers, the light infantry did not stop to pick up their casualties from the fight at the bridge. These casualties included one wounded soldier who had been struck in the head by a colonial with a tomahawk. Word of this atrocity spread rapidly among the regulars, growing well beyond its original facts as the story was told and retold.

In Concord, Colonel Smith was anxiously waiting for the reinforcements he had requested from General Gage eight hours earlier. It was past noon, and Smith could see that the provincials now outnumbered his regulars, with more men steadily streaming in from the countryside. Barrett had moved the rest of his men across the North Bridge, nearly surrounding the regulars. None of these developments pleased Smith. His men had been on the march since before 10 PM the previous night. They carried only 36 cartridges each, and they were seventeen miles from Boston, deep in the hostile countryside with no reinforcements in sight. Smith finally gave the order to march toward Boston, with the grenadiers and marines on the road and the light infantry on each flank to keep the provincials out of musket range.

For the first mile, all was quiet. The regulars and the provincials had exchanged shots earlier on the Lexington Green and at Concord's North Bridge, and a number of men had been killed or wounded, but the provincial forces had acted defensively, not firing until fired upon. When the regulars reached Merriam's Corner, the light infantry protecting the column's flanks had to move in close to use a bridge that crossed a stream. There were perhaps 1,000 minute and militia men waiting for them there. As the regulars crossed this bridge, shooting began again-it is not clear who fired first-which resulted in large-scale firing by regulars and provincials. The provincials took advantage of the fact that the terrain forced the flankers in close to the column. This allowed the provincials to get close enough to use their muskets effectively, while taking advantage of stone fences, rocks and ditches.

One mile down the road British ambush (Hardy's Hill)