Crystal Fortress
The Crystal Fortress was the legendary super-weapon of the Marcon Alliance. Its location is unknown and recorded only in secondary-sources. The most likely explanation is that it was destroyed by the Gudersnipe Army in B.G.A. 301. The Foundation has always remained silent on the matter (both officially and unofficially) and remains of the weapon have never been found.
Purpose
The Court consisted of the 1001 most powerful wizards in the entire Marcon Alliance (including the Emperor). This group of mages had two towers: one at the capitol on Lake Bentika and one at Centered. From these towers, they could cast their most powerful spells.
The problem, then, became getting those spells to a target. The entire court could not be moved whenever a spell was needed, so the Fortress was constructed to act as a way-point. Situated very high above either tower, spells could be redirected to any point on the Greater Continent, or through a portal to other worlds, allowing the court to command the entire empire from the capitol.
Design
Information on the tower comes only through secondary-sources, but it is described as a floating island with a hole through the middle and eight smaller towers. Likely constructed of White Ivory and reinforced with other magical materials. The Fortress would have been operated by low-level expendable mages and Strawmen. More powerful wizards would operate the portals and maintain the flight capabilities. The Fortress was manned year-round and at all hours, and could even be used to cast smaller spells when the entire Court was not needed.
The Fortress would only have been reachable by SkyShip.