The "gate," built in 52 AD by the emperor Claudius, was originally intended to provide a decorative section of support for two aqueducts, the Aqua Claudia and the Anio Novus.

At that time these aqueducts crossed the ancient Via Labicana and Praenestina roads thereby providing the opportunity to create at this location a sort of triumphal arch to the conquest of nature and its conqueror, the emperor Claudius.

Experts refer to this as an early example of “architectural recycling,” essentially adapting one existing structure to another use, in this case using an aqueduct as a wall.

The following inscriptions in praise of the emperors Claudius, Vespasian, and Titus for their work on the aqueducts are prominently displayed on the attic of the Porta Maggiore:

The groundplan shows three naves and an apse, a design similar to that which began to be adopted in Christian basilicas during the 4th century.