(v) _There should be facilities for cover_ on the position and concealed avenues of approach from the rear. A crest affords cover on the reverse slopes and woods provide concealment, while time enables artificial means to be adopted. Tactical cover can be provided by cavalry and advanced troops in the early stages of manoeuvre-battle, and in removing this cover the troops can withdraw in such a way as to lure the enemy on {89} to a false position. They can also induce premature deployments by the enemy, and movements across the front of the real position. (vi) _There should be good artillery positions_ to provide effective fire on all hostile avenues of approach, and counter-battery work on hostile artillery positions. There should also be firm ground and good roads for the movement of guns, and an absence of landmarks for the enemy to range on. Guns of the heaviest calibre take part in all modern battles, their disposition being settled in conference with the artillery commander. A battery of field artillery requires 100 yards frontage for its six guns, and there is usually an interval of 25 yards between batteries. (vii) _There must be depth_ to allow for the disposal and movement of the Supports and Reserves, and for manoeuvres to recapture the forward defences, or to issue to the counter-attack. (viii) _There must be good lateral and frontal communication_ in order that any part of the line can be quickly reinforced. A position astride an unfordable stream, or high ridge or deep ravine should therefore be avoided. At the _Battle of Dresden_ (August 26, 1813) the Allies were encamped on the left bank of the Elbe. Their forces were posted on the heights, but the position was cut transversely by a deep ravine, so that the left wing was isolated from the centre and right. This vicious disposition did not escape the penetrating eye of Napoleon, who attacked their isolated wing with superior forces and routed it completely, with the capture of 10,000 prisoners, before any assistance could arrive. The task of creating lateral communications, if none exist, is of the utmost importance, as they enable a commander to achieve the primary object of every military manoeuvre, to meet the enemy with superior forces at the desired point.