Longfellow's famous poem is inaccurate, and long, but still enjoyable.
Listen my children and you shall hearIt goes on for a considerable length.
Of the midnight ride of Paul Revere,
On the eighteenth of April, in Seventy-five;
Hardly a man is now alive
Who remembers that famous day and year.
He said to his friend, “If the British march
By land or sea from the town to-night,
Hang a lantern aloft in the belfry arch
Of the North Church tower as a signal light,–
One if by land, and two if by sea;
And I on the opposite shore will be,
Ready to ride and spread the alarm
Through every Middlesex village and farm,
For the country folk to be up and to arm.”
The reality is that Revere was one of many riders, many of whom made it much further in giving the alarm than Revere. Further, there is no basis for the quote that Revere was yelling "the British are coming, the British are coming". Quite the opposite, Revere was notifying specific people, as quietly and surreptitiously as possible, trying NOT to let the British troops stationed in the area from being aware of that notification. The popular inaccuracy completely misses the stealthy nature of this event.
From wikipedia, which did a good job of covering the actual, factual event, since this particular entry is so well researched and documented, and provides an excellent larger context:
In the days before April 18, Revere had instructed Robert Newman, the sexton of the North Church, to send a signal by lantern to alert colonists in Charlestown as to the movements of the troops when the information became known. In what is well known today by the phrase "one if by land, two if by sea", one lantern in the steeple would signal the army's choice of the land route while two lanterns would signal the route "by water" across the Charles River. Revere first gave instructions to send the signal to Charlestown. He then crossed the Charles River by rowboat, slipping past the British warship HMS Somerset at anchor. Crossings were banned at that hour, but Revere safely landed in Charlestown and rode to Lexington, avoiding a British patrol and later warning almost every house along the route. The Charlestown colonists dispatched additional riders to the north.Riding through present-day Somerville, Medford, and Arlington, Revere warned patriots along his route, many of whom set out on horseback to deliver warnings of their own. By the end of the night there were probably as many as 40 riders throughout Middlesex County carrying the news of the army's advance. Revere did not shout the phrase later attributed to him ("The British are coming!"): His mission depended on secrecy, the countryside was filled with British army patrols, and most of the Massachusetts colonists (who were predominantly English in ethnic origin) still considered themselves British. Revere's warning, according to eyewitness accounts of the ride and Revere's own descriptions, was "The Regulars are coming out." Revere arrived in Lexington around midnight, with Dawes arriving about a half hour later. They met with Samuel Adams and John Hancock, who were spending the night with Hancock's relatives (in what is now called the Hancock-Clarke House), and they spent a great deal of time discussing plans of action upon receiving the news. They believed that the forces leaving the city were too large for the sole task of arresting two men and that Concord was the main target. The Lexington men dispatched riders to the surrounding towns, and Revere and Dawes continued along the road to Concord accompanied by Samuel Prescott, a doctor who happened to be in Lexington "returning from a lady friend's house at the awkward hour of 1 a.m."
Revere, Dawes, and Prescott were detained by a British Army patrol in Lincoln at a roadblock on the way to Concord. Prescott jumped his horse over a wall and escaped into the woods; he eventually reached Concord. Dawes also escaped, though he fell off his horse not long after and did not complete the ride.
Revere was captured and questioned by the British soldiers at gunpoint. He told them of the army's movement from Boston, and that British army troops would be in some danger if they approached Lexington, because of the large number of hostile militia gathered there. He and other captives taken by the patrol were still escorted east toward Lexington, until about a half mile from Lexington they heard a gunshot. The British major demanded Revere explain the gunfire, and Revere replied it was a signal to "alarm the country". As the group drew closer to Lexington, the town bell began to clang rapidly, upon which one of the captives proclaimed to the British soldiers "The bell's a'ringing! The town's alarmed, and you're all dead men!" The British soldiers gathered and decided not to press further towards Lexington but instead to free the prisoners and head back to warn their commanders. The British confiscated Revere's horse and rode off to warn the approaching army column. Revere walked to Rev. Jonas Clarke's house, where Hancock and Adams were staying. As the battle on Lexington Green unfolded, Revere assisted Hancock and his family in their escape from Lexington, helping to carry a trunk of Hancock's papers. The ride of the three men triggered a flexible system of "alarm and muster" that had been carefully developed months before, in reaction to the colonists' impotent response to the Powder Alarm of September 1774. This system was an improved version of an old network of widespread notification and fast deployment of local militia forces in times of emergency. The colonists had periodically used this system all the way back to the early years of Indian wars in the colony, before it fell into disuse in the French and Indian War. In addition to other express riders delivering messages, bells, drums, alarm guns, bonfires, and a trumpet were used for rapid communication from town to town, notifying the rebels in dozens of eastern Massachusetts villages that they should muster their militias because the regulars in numbers greater than 500 were leaving Boston with possible hostile intentions. This system was so effective that people in towns 25 miles (40 km) from Boston were aware of the army's movements while they were still unloading boats in Cambridge.
Unlike in the Powder Alarm, the alarm raised by the three riders successfully allowed the militia to confront the British troops in Concord, and then harry them all the way back to Boston.