The Battle of Yorktown or Siege of Yorktown was fought from April 5 to May 4, 1862, as part of the Peninsula Campaign of the American Civil War. Marching from Fort Monroe, Union Maj. Gen. George B. McClellan's Army of the Potomac encountered Maj. Gen. John B. Magruder's small Confederate force at Yorktown behind the Warwick Line. McClellan suspended his march up the Peninsula toward Richmond and settled in for siege operations.