On April 5, the IV Corps of Brig. Gen. Erasmus D. Keyes made initial contact with Confederate defensive works at Lee's Mill, an area McClellan expected to move through without resistance. Magruder's ostentatious movement of troops back and forth convinced the Union that his works were strongly held. As the two armies fought an artillery duel, reconnaissance indicated to Keyes the strength and breadth of the Confederate fortifications, and he advised McClellan against assaulting them.