The Warwick Line (also known as the Warwick–Yorktown line) was a defensive works across the Virginia Peninsula maintained along the Warwick River by Confederate General John B. Magruder against much larger Union forces under General George B. McClellan during the American Civil War in 1861–62.
The main line extended 12 miles from Yorktown to the Warwick River and downstream to Lee's Mill, then westward to Skiffe's Creek, which flowed into the James River at Mulberry Island, where the line was anchored on the east by a four-gun battery at Mulberry Island Point. The south end of Mulberry Island (now part of Fort Eustis) is located at the confluence of the Warwick and James Rivers.
Through elaborate ruse tactics, "Prince John" Magruder, who was also an amateur actor, deceived McClellan and held the line for about 30 days, a delay which helped provide valuable time for the ultimately successful defense of Richmond led by General Robert E. Lee, prolonging the war almost three additional years.