FIRST STRONGHOLD is played on a 27 ft. by 54 ft. field. Each alliance commands one tower, five defenses, and a 'secret passage' which allows their robots to restock on ammunition, called boulders.
One defense in each alliance's set of five, the low bar, is a permanent part of the field. Three defenses are selected strategically by the alliance prior to the start of their match. The final defense changes periodically by audience selection.