On the approach of the besiegers, the governor set fire to the town and retired to the forts, and, in answer to the summons to surrender, replied that "it would be time enough to talk about that a month hence." Marlborough ordered General Tettau to cross the river in boats, with eight hundred picked men, and to carry Old Fort by storm.

The assault was made with great determination and bravery; but the works were strong and stoutly defended, and the British were about to fall back, discomfited, when fortune came to their assistance.

Some loose powder ignited and fired the magazine, by which more than two hundred men of the garrison were killed, and the works seriously injured.

After this disaster, the governor abandoned the fort and withdrew, with the survivors of its garrison, to Charles's Fort.

Marlborough at once commenced the siege of this position, but for fifteen days the place resisted all his efforts.
The heavy loss, however, which the garrison had suffered by the explosion in Old Fort, rendered them unable, by sallies, to interfere with the works of the besiegers.