Why did General Anderson surrender fort Sumter?

Major Anderson, commander of the U.S. army unit in Charleston, South Carolina, at the time that South Carolina seceded from the Union, moved his troops into Fort Sumter in 1860 for two reasons. First, as the Civil War loomed, he had remained loyal to the Union despite being stationed in the heart of what was soon to become the Confederacy. Second, in his attempt to hold his position in Charleston, he judged accurately that Fort Sumter, located in the center of the harbor, would be the most defensible point in which to station himself and his troops.