This was the site of one of the first skirmishes in the Revolutionary War. During the battle at Concord, about 90 British soldiers held this bridge while several hundred militiamen gathered on the hill nearby. The British were expecting resistance from disorganized farmers, so when the rebels advanced in a "very military manner", the British panicked. Angry farmers are terrifying at the best of times. Officers gave conflicting orders, the British formations broke and the soldiers ran away.
The original bridge was torn down in 1788 and a new bridge was built nearby. Of course, it's been rebuilt several times - the image of the British turning tail is excellent fodder for historical re-enactments, which Americans enjoy re-enacting, but which never seem to be re-enacted on our side of the Atlantic. Strange, that.