On May 24-27, Union forces built a distinctive network of earthworks known as the “V’s” as part of their defense in this area. The first trenches, on the right, were hastily constructed by Crawford and Crittenden's divisions after they were isolated following the repulse of Ledlie's brigade, forming a horseshoe-shaped line with its flanks anchored on the steep banks of the North Anna. A second trench line branching to the left was built by Crawford's Pennsylvanians and the remaining 5th Corps divisions marching to their rescue on May 25, and it was improved until the Federal forces withdrew from the North Anna River on May 27. After these earthworks were completed, Lee lost any opportunity to strike a decisive blow against the Union army here. Fierce skirmishing occurred in the wooded area behind the lines, but no Confederate attack was made. Though still commanding the Army of Northern Virginia, General Lee was confined to his tent by a virulent attack of diarrhea and repeatedly said, "We must strike them a blow, we must never let them pass us again, we must strike them a blow."