The shot heard 'round the world continues to reverbate. Each April, Massachusetts and Maine celebrate Patriots Day in honor of the battles and skirmishes that began our fight for independence. This year, Patriots Day is April 20 - except in Concord, where they'll celebrate it on the real day: April 19.

Yes, they take their Patriots Day seriously in Concord. On Patriots Day, troops of Minutemen assemble at dawn in Concord and surrounding towns to recreate the "line of march" to the Old North Bridge, Emerson's "rude bridge," where they face off in a gunbattle with a troop of Redcoats. Guess which side always wins? Take a virtual trip over to Concord for an online roundup of the day's events.

You can learn more about the history of the battles of Lexington and Concord thanks to the Military Science department at Worcester Polytechnic, or see what there is to do in Minute Man National Historical Park.

Of course, the battle did not just happen in a vacuum - friction between the colonies and England had been building for years. By 1775, Boston was a hotbed of radical agitation - remember the Boston Tea Party. Today, the city maintains the Freedom Trail to guide visitors around the city's Revolutionary hot spots. Virtually Boston offers the Online Freedom Trail to show you what you'll see when you come to town, as well as a series of articles on the events leading up to April 19. Some of the sites on the trail are part of the Boston National Historical Park.

Technically, the events commemorated on April 19 or thereabouts actually started the night before, around 10 p.m., to be exact. That's when that famous light was set in Boston's Old North Church to signal to Paul Revere and others that the British were on the move to capture an arms cache in Concord, some 15 miles to the west.

At the center of much of the mythology surrounding Patriots Day, of course, is Paul Revere. Revere was immortalized by Longfellow's poem (you know: "Listen my children and you shall hear of the midnight ride of Paul Revere ..."), not to mention a Grant Wood painting. And never mind that much of the poem is simply inaccurate (see also this page for more on that) or that Revere was actually only one of several riders that night (in fact, the British captured Revere early on, leaving it to William Dawes and Samuel Prescott to get to Concord).

For despite all this, Revere was a fascinating man, well worth the attention of historians. Not only did he live in Boston's oldest house, he was an accomplished silversmith. In 1779, he was court-martialed for his action (or inaction) in a disastrous naval battle in Maine. And he was also an artist and poet. In fact, given the inaccuracies in Longfellow's poem, it is ironic that Revere himself perpetuated inaccuracies in a print and poem depicting the Boston Massacre that helped to turn some colonists against the British.

In more recent years, another event held on Patriots Day has tended to get more attention than the Revolutionary rembrances. It's a real heartbreaker.