It is one of the most grandiose architectural complexes of the city. It is formed by a great platform in the form of a wall, whose dimensions are 400 m per side, which perfectly delimits a wide rectangular space that houses the Temple of the Feathered Serpent, also known as the Temple of Quetzalcoatl. A large plaza, a shrine in the center of the plaza and two residential units complete the complex of La Ciudadela. The polychrome remains of painting that are preserved both in the reliefs of the facades of the temple, as in the walls of the constructive levels of greater antiquity of the residential groups stand out.

Temple of the Feathered Serpent: The Temple of the Feathered Serpent is one of the oldest in the city and undoubtedly one of the most beautiful, originally built on seven architectural levels with the talud-tablero design typical of this city. This design presents a singular decoration composed by a series of sculptures of two divine monsters alternating in the board, while in the slopes of each body, carved in low relief, there is a feathered serpent in profile; in both cases they present a background with a representation of marine elements, and apparently the four facades had the same decoration. The building is of solid construction, of stones with mud, and in the foundations of the temple a series of offerings were registered that contained mainly human remains; these offerings are dedicated to the construction of the building or to the deity. In the Museum of Teotihuacan Culture there are two reproductions of these offerings, which represent a clear sample of the human sacrifice practiced in Teotihuacan for religious purposes.

Cosmogonic-calendrical signs: The panels of this building were decorated with circular designs framed by crisscrossed bands, which have been interpreted as signs of the four directions or the quincunx.