The catacombs are remains of the original Heimdallr, which was founded in circa S.170.[Note 1]
In S.371, Dark Dragon Zoro-Agruga invaded and occupied the city, spreading its miasma throughout the capital that turned Heimdallr into a city of the dead. Zoro-Agruga desecrated the corpses of the fallen, taking control of their bodies and using them to attack those who remained alive, further increasing its legions of the dead. When Emperor Hector I managed to retake the city a century later, Heimdallr had become a necropolis. Emperor Hector I's successor decided to build a new Heimdallr over the ruins of the old one.
It is rumoured that the spirits of people who got lost in there hundreds of years ago are still lurking about.