It is built within a natural cliff resting at the eastern border with Crossbell, from which the Garrelia looks like an enormous wall. Apart from a tunnel, through twice the Transcontinental Railroad runs, two enormous orbal railway guns developed by Reinford can be seen. The Training Grounds near the Garrelia Fortress are used for military exercises of the Imperial Army of Erebonia.
The railway cannons are known as the mightiest weapons wrought by the hands of man since the Great Collapse. They are considered to have the longest range of any orbal cannon in the world, capable of targeting any point within Crossbell. Their destructive power could wipe out Crossbell City and its 500,000 citzens within a couple of hours.
The railway cannons were originally developed by the Reinford Group under supervision of chairman Gwyn Reinford and signed by Professor G. Schmidt. Upon completion in S.1199, he realised that he had been constructing instruments of massacre. Gwyn regretted his decision and was hesitant over whether to hand the guns over to the Imperial Army. Behind his back, his daughter Irina Reinford secured the support of all Reinford's major shareholders, from Nortia Porvince's ruler Marquis Rogner to the top brass of the Imperial Army. Pressured, Gwyn stepped down as chairman and was immediately succeeded by Irina, the current chairman.
It is not known when construction on the Garrelia Fortress started nor when it was finished.
The Garrelia Fortress was destroyed on 24 October S.1204 at 16:21 by Aion Type-α, a newly developed humanoid weapon by Ouroboros' Thirteen Factories and bought by then president Dieter Crois of the Independent State of Crossbell.
After Crossbell's declaration of independence, both Erebonia and Calvard sent military units to infiltrate Crossbell. In response, Crossbell defended itself by having the Aion Type-β and Aion Type-γ destroy the Erebonian and Calvardian units, respectively.
Erebonia immediately prepared its next attack by readying the railway guns. Each fired one shot. The first was blocked by the Aion Type-α and the second was erased from existence with the power it received from the Azure Demiourgos. The Aion then proceeded to use that same power to teleport to Garrelia Fortress and remove the entire installation surrounding the railway cannons from existence.
The men and women of the 5th Armored Division stationed at the base disappeared with it. The surviving members of the Divison re-grouped at the Training Grounds near the Fortress and Warrant Officer Arbekker took over Lieutenant General Walter's duty, who was present in the Garrelia Fortress at the time of the attack.
Shortly after the Garrelia Fortress had been ruined, the cryptid Volglyph manifested in the area.
Two months later, when the Azure Tree vanished alongside the Azure Demiourgos, the disappeared members of the 5th Division reappeared, unharmed.