Earthworks and Breastworks
After receiving information about the proximity of the enemy troops, both sides began to construct earthworks and defenses as well as taking advantage of natural defenses. Union forces dug trenches and constructed breastworks at Culp's Hill and Cemetery Hill. Also, Union forces positioned themselves along Cemetery Ridge, a position that offered a good defensive spot. This would become a primary defensive position as the battle progressed.
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Reconnaissance
Neither the Army of the Potomac nor the Army of Northern Virginia had time to perform much reconnaissance. However, Lee's attempt to do so seriously crippled his army, when he sent J.E.B. Stuart and the Cavalry Corps away to scout behind Union lines. Stuart was gone for most of the Battle of Gettysburg, and consequently, Lee lost the use of his cavalry. The reconnaissance that was performed was often by the South, and was done to give an idea of the strength of the Union forces and where they were positioned.