Fortress was a title originally in development at the now defunct Swedish development studio GRIN. The game was intended to be a third person action title set in Square Enix's Ivalice universe that had a strong emphasis on tactical combat in the vein of a Devil May Cry or Dark Souls. The game would have featured a nonlinear campaign and Nordic inspired aesthetic.
The game was intended to serve as a sequel to Final Fantasy Xii, featuring Basch fon Ronsenburg as the main playable protagonist. Basch's Magister unit would be tasked with defending a Fortress from regular onslaughts of an undead horde lead by the Sea King Leomund who rises every 10,000 years to attempt to reclaim his crown hidden in the Fortress. The game would progress through 8 seasons as Basch attempts to bolster his forces, navigate personal relationships among denizens of the Fortress, maintain the Fortress through forays to gather resources from local surrounding areas, all the while fending off nearly relentless Undead horde incursions from scouring Ivalice. Familiar FFXII faces such as Queen Ashelia B'Nargain Dalmasca, Larsa Ferrinas Solidor and Balthier were all scheduled to have major roles in the game.
However, in 2009 Square Enix reportedly forced GRIN to stop development on the project by withholding payments due to a communication breakdown and reportedly strong creative differences over art direction. According to Ulf Andersson, former co-head of GRIN, Square Enix cancelled the project due to concerns that GRIN did not have adequate cashflow viability to be able to deliver the project to fruition given their large head count, recent releases of commercial and critical failures as well as a complete lack of other projects to sustain them during Fortress's development. Whatever the actual reasons were, this circumstance ultimately lead to the game's likely cancellation (as of 2011 Square Enix only officially has acknowledged an indefinite delay) as well as GRIN's bankruptcy and dissolution.
If Fortress had been released it would have been the first Final Fantasy game ever developed outside of Japan.
[Source Gamespot: http://www.gamespot.com/articles/the-story-behind-fortress-the-final-fantasy-game-t/1100-6431036/