After the battle at Concord on 19 April 1775, the British beat a hasty retreat back to Boston.  With American colonists hot on their heels and taking potshots at them from behind rocks and trees, they could not wait to get back to the relative safety of Boston. But the militia that had taken such a deadly toll did not retire once the British reached their base.  Instead they set up camp just outside the city and dared the British to come out and play.  

British General Thomas Gage eyed the growing American force with considerable alarm.  Their numbers grew by the day.  But he knew that within the fortified city his troops were relatively safe from the thousands of colonial militia on the other side of the Charles River.  He also realized, however, that the city would be vulnerable if the colonial militia were to occupy the high ground outside the city—in particular, Dorchester Heights to the south. Canons placed on those hills could cherry-pick the British barracks and ships inside the city below.  Therefore he made plans to seize the high ground on 17 June.  

Informed of their plans (the Americans had spies everywhere), militia officers Israel Putnam and William Prescott convinced a reluctant General Artemas Ward to fortify the high ground to the north of the city, a cluster of hills including Breed’s and Bunker Hill. On 16 June, Prescott and a force of about 1000 men constructed, under the cover of darkness, a six-foot earthen wall along the crest of Breed’s Hill (the hill closest to the Charles River and the city of Boston).  Militia also reinforced a rail fence to the north of the hill to protect the Americans’ left flank.

On the morning of 17 June, the British woke to the new American defenses.  Realizing just how vulnerable they now were, they immediately opened fire (largely ineffective) from ships in the harbor. At noon, a force of 2200 under General William Howe landed at Mouton’s Point, east of the American defenses.  Their advance was initially slowed by swampy terrain, tall grasses, and fire from both the hill and the village of Dorchester to the south. But methodically they marched toward the American lines. 

As the battle-hardened British column approached, the American militia remained surprisingly calm.  According to legend, Prescott instructed his men not to fire “until you see the whites of their eyes.”  At fifty yards, the Redcoats dilated pupils came into view and the colonial militia let loose a withering musket fire.  The British fell back within minutes, stunning the seasoned British commander, William Howe.  “It was” he later remarked, “a moment that I never felt before.”

Nevertheless, Howe ordered a second assault. Some British troops came within one-hundred feet of American lines, but they too suffered heavy casualties and were forced to retreat. 

Repelling this second assault, however, consumed most of the Americans’ gun powder and bullets.  The Redcoats' third attack, consequently, succeeded in overrunning the American lines and forcing the American militia to withdraw.  The British took the hill, but they were too demoralized and disorganized to pursue effectively, allowing most American militia to escape.

The British therefore won the battle but suffered high casualties, far more than they had anticipated against the green American militia.  The American militia, on the other hand, walked away from the battle with the sense that the celebrated British army was not invincible.  Perhaps most ironically, having spent so much to take the high ground to the north of the city, the British never seized the high ground to the south.  On 4 March 1776, General George Washington ordered the canon, recently seized at Fort Ticonderoga, placed on Dorchester Heights.  Within weeks, the British were forced to withdraw from Boston.