In The Lord of the Rings: The Return of the King, the city beneath Mount Mindolluin is Minas Tirith.
Minas Tirith is the capital of Gondor and the main target of Sauron’s assault in the film’s central battle. Its seven ascending levels are protected by walls and culminate in the Citadel, where the Steward Denethor rules while Aragorn’s claim to the throne remains unresolved.
The city was originally called Minas Anor, meaning “Tower of the Sun.” After the fall of Minas Ithil to Sauron’s forces, Minas Anor became known as Minas Tirith, “Tower of Guard.” Osgiliath is another Gondorian city nearby, while Minas Morgul is its corrupted counterpart.