Not until around 10 P.M. on the night of 19 April, twenty-four hours after they had first mustered for their march to Concord, are all the Regulars back in Boston, having been ferried from Charlestown on the last leg of their mission. Over the next few days, a force of approximately 20,000 provincials, intent on preventing Gage's troops from making any more forays into the countryside, lays siege to the town. In the ensuing weeks, as colonists drift back toward their homes, Joseph Warren, president pro tempore of the Provincial Congress then meeting at Watertown, urges his colleagues to act boldly and to do so immediately.