The Battles of Lexington and Concord began almost by accident. Following the revelation that the military governor of Massachusetts, Gen Thomas Gage, intended for British Army regulars to confiscate arms and ammunition from Massachusetts militia units based out of Concord, the local militia began to sound the alarm and muster. In the early hours of 19 April 1775, British forces under LtCol Francis Smith, numbering around 700 men, departed in the direction of Concord. Upon reaching Lexington, the regulars were met by around 80 members of the local militia. As the militia began to disperse, a shot from an unknown source was fired—prompting both sides to fire upon each other. A bayonet charge dispersed the militia, and the regulars then proceeded toward Concord. Upon reaching Concord, the regulars dispersed through the town to scour for militia armaments and secured positions around the North Bridge. While this was occurring, the colonial militia began forming in the heights overlooking the North Bridge and began moving toward Concord. After a brief exchange of fire, both sides withdrew, and the regulars continued to search and destroy militia supplies before beginning their return to Boston around midday. As the regulars embarked on the road to Boston, hundreds of local militiamen—using guerilla tactics—proceeded repeatedly to assault, ambush, and delay the main column at any possible opportunity, with their numbers increasing to several thousand by the end of the day. A relief force from Boston reinforced the regulars as they passed through Lexington, but failure to bring an ample supply of ammunition forced the regulars to continue their withdrawal to Boston. The regulars were pursued to Charlestown, where they were able to command a strong defensive position. The Battles of Lexington and Concord proved that a disorganized but determined militia could outmaneuver and bring superior arms to bear against an organized regular force. Ultimately, colonial casualties numbered less than 100, whereas the regulars suffered around 300 total losses.