Once Confederate forces were routed in February, 1862, from Forts Henry and Donelson (on the Tennessee and Cumberland Rivers, respectively), Confederate commanders decided that any further effort in the defense of Nashville would be pointless, and they abandoned any attempt to keep Nashville behind their lines. It was almost immediately occupied by Union forces, who rapidly began preparations for its defense. The largest of the fortifications erected was Fort Negley, a star-shaped limestone block structure atop St. Cloud Hill, south of the city. The construction of the fort was overseen by Captain James St. Clair Morton. The fort was constructed out of of stone, of earth and cost $130,000. It was largely constructed using the labor of local slaves (including women), newly freed slaves who had flocked to Nashville once it was taken by Union forces with the understanding that their status as slaves was to be revoked were they to work for the Union, and by free blacks forcibly conscripted for the work. Records show that 2,768 blacks were officially enrolled in its construction. The fort was named for Union Army commander General James S. Negley.