Khoven
Located in the centre of the First Quarter is the Crater of Khoven, formerly the city of Khoven.
When it stood, Khoven was a city-state that fully embraced arcane magic. Filled to the brim with powerful arcane wizards, a veritable anomaly on account of arcane magic's tendencies to induce paranoia in its users. While it stood, its populace supplied the vast majority of Sevess' arcanely enchanted materials, and served as a central transport hub for its few scattered allies.
As a city state, they remained mostly neutral. The population was only able to remain as stable and free of worldwide political turmoil as it did for so long on account of its thorough vetting of arcane wizards. Only those with the deepest of drives for research were given leave to augment themselves and pursue the mind-muddling power that arcane implants could grant, staving off the desire to isolate and accumulate power for as long as was feasibly possible.
But even that did not save it indefinitely. The city suffered a very ironic destruction at the hands of a Khovian Detonation - named such for the research and definition done by the city's founder, Khoven. Khovian detonations are the result of the sudden offloading of energy that occurs when an arcane wizard's internal state is thoroughly disrupted, usually due to death. The energy stored is released, violently. The more powerful the wizard, the larger the detonation.
Khoven did have measures in place to prevent this from happening within the city walls. However, due to reasons that have been largely lost in the city's destruction, these did not trigger on the day of the detonation.
Hundreds of powerful wizards in close proximity to each other. One dies suddenly. It does not take much imagination to discern what followed, and why a crater lays where the city once stood.