Reverse Slope defense: Military Tactic

A reverse slope defence is a military tactic where a defending force is positioned on the slope of an elevated terrain feature such as a hill, ridge, or mountain, on the side opposite from the attacking force. This tactic hinders both the attacker's ability to observe the defender's positions as well as the effectiveness of the attacker's long-range weapons, such as tanks and artillery.

A defending unit usually does not conduct a reverse-slope defence along its entire front; however, there are situations where subordinate units and weapon systems may be positioned on the reverse slope. This may be a wise choice when enemy forces have superior long-range direct-fire or indirect-fire weapons. The defending force uses the hill to limit enemy observation reducing the effectiveness of long-range enemy fire. It may even succeed in deceiving the enemy as to the true location and organisation of the main defensive positions. As the attacker advances and passes over the top of the hill, he may be ambushed by short-range fire from the defender.

Napoleonic Wars
The most well-known proponent of the tactic was the Duke of Wellington who used it repeatedly during the Napoleonic Wars to defeat the French infantry tactic of attacking in columns. By placing a ridge between his own army and his opponent's, and having his troops lie down, Wellington was able to both protect his troops from French artillery fire and to surprise the attacking French infantry by having his troops stand up at the last moment and deliver volleys of musketry at close range. So often were the French beaten in this manner it prompted Wellington to comment, "They came on in the same old way and we defeated them in the same old way".