The Battle of Alligator Bridge took place on June 30, 1778, and was the major engagement in Colonel Elijah Clark's third, and final, unsuccessful campaign to conquer East Florida. In a disastrous battle, Clark's 300 Georgia militiamen went up against a far larger force composed of British regulars, Tories, and Indians. As with previous failures in the region, Southern politicians refused to grant Continental Army officers full command of their militias. So, while General Robert Howe waited to the north, at Fort Tonyn, with 400-odd regular troops, waiting for Georgia's governor John Houstoun and South Carolina general Andrew Williamson to arrive with their militias, Clark pursued an enemy detachment that had just been routed from an outpost to the west of the fort. He and his men were stopped at Alligator Bridge, where Major Marc Prevost had established hasty field fortifications. In the fortifications were 500 British regulars, along with 200 more outside of them; also outside were around 100 Rangers.

Clark took a detachment of mounted men and attacked what he saw as a weak point in the British line. He expected to break the line and pour the rest of his men into the breach. But the horses had trouble getting through the tangle of brush and logs that had been set up specifically as an obstacle course; when they cleared this, they reached a ditch that was designed for the same purpose. The ditch was too wide for the horses to clear with one jump, and this was the moment the British chose to begin shooting and shouting. Clark was wounded and nearly captured, after which he ordered a recall. (Some say he was spurred on by a counterattack of British troops posted outside of their earthworks.) Whatever the reason, Clark withdrew, having lost nine men killed in action. He lost more to hunger and sickness, leading to the collapse of the 1778 invasion.

The site of the bridge has long been supposed to have been in central Callahan, where a marker has been placed stating as much, but some historians believe that the actual site of the bridge was somewhat farther east.