It was built around the same time that the Helman Empire was founded, in order to prevent invasions from the Demon Army and keep monsters at bay. It has proven effective since its construction, although in the current era the region of the Monster Realm adjacent to the fort is under the control of the Hornet Faction, a non-aggressive group that seeks peaceful coexistence with humanity, so it is not currently under much threat of a full-scale invasion by a Monster Army.
The 2nd Army of the Helman Empire is stationed in the fort and its current general, Aristoles Calm, is in charge of its operations. The fort was designed not only to serve as a barrier, but also as a place for soldiers to live in. Roughly 150,000 soldiers are stationed in the fort, and the garrison is also equipped with heavy weapons such as huge ballistae which fire two meter-long bolts, trebuchets, and monster tamers controlling powerful monsters. While this is fairly impressive, the 500-year-old fort is antiquated compared to Zeth's Maginot Line, and would probably have a hard time holding back a large-scale invasion like the one Kamilla performed on Zeth in LP0003.