The First Battle of Bull Run, also known as First Manassas (the name used by Confederate forces), was fought on July 21, 1861, in Prince William County, Virginia, near the city of Manassas, not far from Washington, D.C. It was the first major battle of the American Civil War. The Union forces were slow in positioning themselves, allowing Confederate reinforcements time to arrive by rail. Each side had about 18,000 poorly trained and poorly led troops in their first battle.