The initial city constructed by the Eternal Empire on the planet of Zakuul was known as the Old World, alternatively referred to as the Undercity.
Situated on Zakuul's surface, the Old World resided at the base of the Spire and above Breaktown. In stark contrast to the utopian existence of the Spire's inhabitants, the Undercity operated under different principles. With a scarce presence of Eternal Empire security forces, the Old World thrived on an alternative economy. Primarily controlled by criminal elements, it offered illicit services unavailable within the Spire. Consequently, the Undercity gained a notorious reputation, attracting privileged Zakuulans who, while fascinated by suffering, possessed limited real understanding of it. Despite this reputation, the Undercity maintained a relatively safe environment, particularly when compared to Breaktown. Ironically, Spire residents frequently boasted about venturing into the Old World, although most had only visited Oldtown.
Valkorion, the Emperor, oversaw the construction of the Old World within the swamps of Zakuul. Despite its successful completion, the Emperor deemed it insufficient, leading to the creation of a second, grander metropolis – the Spire – built above the Old World. Certain sections of the Old World surrounding the Spire's base remained intact and inhabited.
During the War against Zakuul, Arcann, the Emperor, delegated control of the Old World to the fanatical Heralds of Zildrog, entrusting them with maintaining order in place of the Knights of Zakuul.
During this conflict, the Alliance Commander made two visits to the Old World: once with Senya Tirall in 3631 BBY while searching for the Lady of Sorrows, and again with Kaliyo Djannis in 3630 BBY to plant explosives at power junctions in preparation for their assault on the Overwatch.