Bozja Citadel was where the Garlean's first attempt to contact/use Dalamud, and it fired a beam that destroyed an entire city and killed Cid's father. Found this on a reddit post, but it's taken from EE1.
The more interesting part to me is that Bozja is located in Othard, and many people thought it was going to be related to Stormblood's story because of it. Some people were debating on if the Burn itself was actually the remains of Bozja where could be feasible but I think that's more of the focus on repeated primal summoning which is also what the dungeon briefing for 4.4 says as well.