Following the skirmishes at Lexington and Concord in April, 1775 that began the American Revolution, the British Army under military governor Thomas Gage retreated to the safety of Boston. The city was soon surrounded by American militia from several states led by General Artemas Ward. For two months, both armies consolidated their forces and constructed defenses; eventually American troops would outnumber the British by around 16,000 to 11,000 men. The British attempted a breakthrough in June under General William Howe, resulting in the Battle of Bunker Hill, but they were ultimately forced to return to Boston with heavy casualties. On July 2nd, George Washington arrived from Philadelphia and took command of the American forces, now officially the Continental Army. The winter was hard on both armies but the siege continued. Yankee fortifications on the hills around the city were bolstered in November by the arrival of artillery from Fort Ticonderoga, 200 miles away in the heavy snow, under the leadership of Henry Knox. Washington ordered the bombardment of the city on March 5, 1776, and after a few days of heavy artillery fire from Dorchester Heights and other high ground around Boston Harbor, Gage decided to withdraw. His army departed the city with the help of the British Navy and retreated to Halifax, ending the eleven-month siege. The American victory took the focus of the war away from the New England colonies and proved that the new Continental Army, even after their defeat at Bunker Hill, could compel the more experienced British to withdraw from a battlefield.