Fortress is an unauthorised clone of SEGA's Zaxxon, copying many elements of the original game. It was developed by Amcom and published by Pace in 1983 for the BBC Microcomputer. Although, the graphics had to be toned down in quite a major way, the gameplay remained. Fortress followed Zaxxon almost identically with all of the stages mirrored - even the opening wall that you must squeeze through. The problem with Fortress was that it was even harder than Zaxxon. It was incredibly difficult to get involved with the game, as it was truly a challenge to stay alive for more than a minute or so. Despite this, Fortress was something of a one-off for the BBC, with no other software house ever trying to copy the Zaxxon game