"Fortress" was recorded at Silo Studios in Hamilton, Ontario during the summer of 2007. The album contains 10 tracks broken into three movements, separated by piano interludes, and is approximately 41 minutes in length. The band has stated that the sound is similar to "Kezia" but with a "less poppy and more technical metal" influence. "Fortress" does not revolve around a single concept, unlike their previous album. Instead, it is more akin to "goddess worship in the tradition of Robert Graves," according to their bassist and lyricist Arif Mirabdolbaghi: