Stronghold: Crusader is the successor to Firefly Studios's 2001 game Stronghold. Crusader has much in common with the original Stronghold, but differs from its predecessor in the fact that the game is no longer set in a pseudo-Europe, instead being set in the Middle East during the Crusades. The game features several new Arabian units that can be purchased in a new building, the mercenary post. Though the Arabian troops do not require any resources to produce, they are rather expensive. The game was also released as Stronghold Warchest. This version was a compendium of Stronghold and an enhanced version of Stronghold: Crusader, containing additional characters and an additional Crusader Trail. Stronghold Crusader features several real-time strategy campaign strings. These document the First, Second and Third Crusade, as well as conflicts within the individual Crusader states. Each campaign comprises several battles, such as Nicea, Heraclea, siege of Antioch, Krak des Chevaliers and the Siege of Jerusalem. The game also features the Crusader Trail, a series of 50 linked missions against various opponents. Stronghold Warchest adds one more Crusader Trail, consisting of 30 linked missions. In 2008, in the game Stronghold Crusader Extreme, another "Extreme" Crusader Trail was incorporated into the game, consisting of 20 linked missions. The gameplay is similar to the original Stronghold, the major difference being that the game is set in the Middle East. As a consequence, farms can only be built on oasis grass, which leads to rivalry among players for limited farmland and resources. The game adds new AI opponents (the number depending on the version of the game) and several new Arabian units purchasable from a mercenary post. The color of the player's units have also been changed from blue to red in order to match the colors of the Knights Templar.