General Thomas Gage, the commander of all British troops in North America and the appointed governor of the Province of Massachusetts had been instructed to stomp out all vestiges of rebellion in the colonies, especially Massachusetts. The crown had disbanded the elected provincial government, and the colonists had responded by creating a rogue provincial congress of their own which moved about from place to place to avoid being broken up General Gage's forces.
Gage's plan was to 1) seize stores of gun powder, munitions and weaponry thereby hamstringing colonial resistance and 2) capture the most prominent leaders of the opposition. He had already made several attempts to grab military supplies, one successful (at the Provincial Powder House) and two unsuccessful (at Portsmouth, New Hampshire and Salem, Massachusetts). On April 19, 1775, he planned to grab the supplies reportedly stored at Concord. In fact, those supplies had already been moved out and hidden away deeper in the countryside. He also wanted to capture two leaders, John Hancock and Samuel Adams, who had been attending the Provincial Congress which had been meeting in Concord and who were laying low in Lexington at the home of the local clergyman. Gage's spies had told him that the best route to Concord was through Lexington.
The colonists had their own spies and were well aware of what Gage was planning. As soon as they knew for sure when Gage was going to set his plan in motion, they triggered the alarm system they had devised to alert the colonial militias. The trick was to get the message out of Boston which was essentially an island and under British control. The plan included express riders to carry the message and signal lights hung in the tallest church spire in Boston ("one if by land and two if by sea"). Revere was one of the riders - he crossed by boat from Boston to Charlestown and rode the northern route to Lexington, rousing the populace along the way. William Dawes took the southern route, across Boston Neck and then on through Cambridge to Lexington. They arrived in Lexington to warn Hancock and Adams before the British troops had even started their march. They then rode on towards Concord to warn that town but were captured by a British patrol. Fortunately, Samuel Prescott, a local doctor, who was riding with them, managed to break away and escape. He carried the message to Concord. Meanwhile, express riders were fanning out all across eastern Massachusetts and by the following day some 4000 militia men were streaming towards Concord and Lexington, vastly outnumbering the British forces.
