Picket duty was an important component of the Union Army’s “Valley Forge.” The infantry picket line extended around the AOP’s 200-square-mile defensive perimeter. To the west and east there were also cavalry picket lines, outposts, and videttes (mounted sentries). Picket duty was rotated regularly and regiments normally served for fixed time periods. Reserves in echeloned infantry positions backed up the pickets. Duty officers at all levels frequently checked the lines. Although contacts were forbidden, Union and Confederate pickets inevitably came into relatively close proximity and communicated with one another. Trading – scarce commodities like coffee for the Confederates and tobacco for the Federals — was the most common contact, where feasible. Occasional discussion or even debates would take place between the lines. Firing on the picket line, of course, was forbidden. Notoriously, when encountering a “new” Union unit, Confederates would pretend to aim their rifles at the Yankee sentries. When they reacted (usually by sensibly taking cover) the Rebels would laugh and ridicule their opponents. Occasionally a deserter would cross the lines and would encounter the picket line. Naturally there was always a chance of a military spy or line-crosser surfacing.