Immediately after the battles of April 19,…
April 1775 CE
They particularly block the Charlestown Neck (the only land access to Charlestown), and the Boston Neck (the only land access to Boston, which is at this time a peninsula), leaving only the harbor and sea access under British control. In the days immediately following the creation of the siege line, the size of the colonial forces grows, as militias from New Hampshire, Rhode Island, and Connecticut arrive on the scene.
General Gage writes of his surprise of the number of rebels surrounding the city: "The rebels are not the despicable rabble too many have supposed them to be....In all their wars against the French they never showed such conduct, attention, and perseverance as they do now."