In the case of the famous ride the British weren’t going to Boston; they were coming from Boston. General Thomas Gage and his roughly 3,000 regulars had been occupying Boston for some time at that point.

Gage had been appointed Governor of Massachusetts and arrived in May 1774. He was supposed to end the unrest in the colony and enforce the intolerable acts (as the Bostonians called them). In September he consolidated many of the regular troops in North America into Boston to give him enough forces to try and bring Massachusetts to heel. But for the most part Gage only really controlled Boston itself; while the Patriots controlled the countryside.

Gage made several attempts to seize and consolidate powder and weapons into Boston. In response the Patriots organized the preexisting militia into cells of “Minutemen” and other militia troops, and developed a system of riders to warn all the cells of any British movement outside of Boston. Revere even made an early ride himself in December from Boston to Portsmouth NH to warn of troops being sent to station there. Local Patriot groups raided Fort William & Mary and confiscated most the supplies before the British arrived. As a response to Gage’s attempts to consolidate powder and weapons into Boston, the Patriots began consolidating it away from the coast, mostly in Concord and Worcester.

That brings us to April 18th, and Revere’s midnight ride. Revere and Paul Dawes had been warned that the British were prepared to take boats across the Charles River (which was really more a part of tidal Boston Bay at that point) to Cambridge and from there inland. So Revere took a rowboat across the mouth of the river himself and rode to the Northwest inland, while Dawes took the land route South across the Boston Neck and from there crossed the Charles River at Cambridge Bridge. Both roused their section and met up with Sam Adams and John Hancock in Lexington, while Samuel Prescott finished the ride to Concord. Thus warned by the riders, the leadership was able to avoid arrest and the military supplies at Concord were moved, and the militia and minutemen were gathered, ultimately leading to the battles of Lexington and Concord.

It should be noted that ultimately whether the British came by land or sea was largely irrelevant. Either way the British were going to head along the same road after leaving Cambridge. And while the initial force lead by Francis Smith came “by sea,” his reinforcements under Hugh Percy marched across the Boston Neck and thus came “by land.” So while an important point in Henry Wadsworth Longfellow’s poem, it was largely irrelevant to how the actual events unfolded.