1. On April 15, 1775, the evacuation of British forces from Boston began, marking the start of the American Revolutionary War. General Thomas Gage, who had been sent to Boston to enforce British rule, became aware of a stockpile of weapons that patriots had gathered in nearby Concord. In response, Gage sent troops to seize the weapons, leading to the famous battles of Lexington and Concord and the start of the war.

2. On April 15, 1783, the first successful flight of a hot air balloon in America occurred in Boston. French inventor Jean-Pierre Blanchard took to the skies in a balloon that had been constructed by John Jeffries, a Boston physician. The flight traveled approximately 5 miles in 46 minutes and was witnessed by a crowd of spectators.

3. On April 15, 1861, President Abraham Lincoln made a call for troops to defend the Union following the attack on Fort Sumter. Massachusetts was one of the first states to respond to the call, with Governor John A. Andrew immediately ordering the mobilization of state militia to support the war effort.

4. On April 15, 1955, the Boston Celtics won their first NBA championship. Led by Hall of Famers Bob Cousy and Bill Sharman, the Celtics defeated the Syracuse Nationals in a dramatic overtime game to take the title. The victory was the first of 17 championships won by the Celtics over the next two decades.

5. On April 15, 2013, two bombs exploded near the finish line of the Boston Marathon, killing three people and injuring hundreds more. The attack, which was carried out by two brothers of Chechen descent, shocked the world and led to a massive manhunt that resulted in the capture of one brother and the death of the other. The city of Boston came together in the aftermath of the tragedy, with residents showing resilience and solidarity in the face of violence.