Fortress was planned to be a huge open-world follow-up to Final Fantasy 12. Developed by Bionic Commando reboot team Grin, it was also the reason for that studio's downfall.
Fortress' existence has been known about since the project was scrapped in 2009. Grin spent half a year on the game, and production artwork and early in-game assets have trickled out ever since.
Now, the largest collection of lost artefacts from Fortress' development has been gathered together by an intrepid NeoGAF user.
Fortress would have returned to Final Fantasy 12's world of Ivalice and included familiar faces such as Ashe, Basch and Larsa.
The game would also have seen "Viking-like" enemy attackers invading from the sea and huge numbers of characters in battle.
Concept artist Tony Holmsten revealed that he and others were not aware of the project's true nature until it was almost cancelled.
"The only thing I can say to us concept artists' defence is that we didn't even know what game/brand it was until the very last two months or something before Grin went bankrupt (I have no idea what Grin's decision behind this was).
"So we had been working several months without any proper art direction just doing something 'fantasy-ish'. And in the end they finally told us what we were doing, and said 'Now we have to remake everything, and make it look more like... ' It was a complete disaster, a shame, it could have been good."
Grin co-founders Bo and Ulf Andersson previously labelled the game's cancellation by Square Enix - which directly preceded the studio's closure - as a "betrayal". At least one report suggested that Square Enix never paid Grin for its work.
Development was supposedly continued elsewhere, but the game never publicly materialised.
The full gallery of artwork and videos is available over on NeoGAF.