On June 13, 1775, the leaders of the colonial forces besieging Boston learned that the British were planning to send troops out from the city to fortify the unoccupied hills surrounding the city, which would give them control of Boston Harbor. In response, 1,200 colonial troops under the command of William Prescott stealthily occupied Bunker Hill and Breed's Hill. They constructed a strong redoubt on Breed's Hill overnight, as well as smaller fortified lines across the Charlestown Peninsula -Wikipedia