The satanic city in Dante’s Inferno is Dis. It is the fortified city enclosing the lower regions of Hell, rather than a separate circle or a biblical city such as Sodom, Gomorrah, or Babylon.
Dante and Virgil approach Dis in Cantos VIII and IX. Its walls are surrounded by the marsh of Styx and guarded by fallen angels, the Furies, and Medusa. An angel eventually opens the gate, allowing the travelers to enter. Inside lie the sixth through ninth circles, where Dante places sins considered more deliberate and malicious.
The name comes from Dis Pater, a Roman god associated with the underworld and often identified with Pluto. Dante drew heavily on Virgil’s Aeneid, in which Aeneas travels through the realm of Dis. Within Dante’s city are heretics, the violent, fraudulent sinners, and traitors, with Satan himself at the center of the deepest circle.
A common mix-up is treating Dis as another name for all of Hell. In the poem, it specifically designates the city and the lower section enclosed by its walls.