Union forces had been constructing defensive works around Nashville since the time the city was occupied in February 1862. By 1864, a 7-mile-long semicircular Union defensive line on the south and west sides of the city protected Nashville from attacks from those directions. The line was studded with forts, the largest being Fort Negley. The trench line was extended to the west after December 1. The Cumberland River formed a natural defensive barrier on the north and east sides of the city. Smith's troops had arrived by river on November 30, and their transports had been escorted by a powerful fleet of tinclad and ironclad gunboats. Thus, the river barrier was well-defended.