The two dominating theories of how to use fortifications in the operational perspective during the 18th and 19th century were the central fortress system () and the peripheral fortress system (), the latter also called the cordon system. The two systems were also known as central defence and peripheral defence. The peripheral defence theory was based on building smaller fortifications in advance positions to meet the enemy at an early stage, while the central defence theory was meant to weaken the enemy step by step in minor skirmishes and ambushes carried out by forces supplied and supported by central fortresses not located in the front line. In short, one theory advocated many minor fortifications built to directly engage the enemy, while the other advocated only a few major fortifications built not to directly engage the enemy, but to support the troops that engaged the enemy.