counterscarp

thumb|right|Counterscarp of a Napoleon era polygonal fort ([[Fort Napoleon, Ostend). Counterscarps had become vertical by this time. The housing at the bottom of the ditch is a caponier from where the defenders could fire on attackers that managed to climb down into the ditch, while being protected from cannon fire themselves.]]

A scarp and a counterscarp are the inner and outer sides, respectively, of a ditch or moat used in fortifications. Attackers (if they have not bridged the ditch) must descend the counterscarp and ascend the scarp. In permanent fortifications, the scarp and counterscarp may be encased in stone. In less permanent fortifications, the counterscarp may be lined with paling fence set at an angle so as to give no cover to the attackers, but to make advancing and retreating more difficult.