While battles were traditionally fought on vast, open landscapes, there were exceptions and a clever strategist could use these to his advantage. Terrain was an effective form of defence, with high ground, woods and forests used to protect the rear and flanks of an army, particularly when faced with a cavalry-heavy opponent. Such features also offered cover for ambush attacks, and knowledge of their terrain became a key factor in the success of the Germans and Gauls who used guerrilla tactics to counter the organised ranks of the Roman army.
