The Porta Maggiore is by far the best urban site to visit for an understanding and view of the ancient aqueducts. It is a monumental double archway built of white travertine. It was first known as the Porta Prenestina, perhaps a reference to the road over which is passes. 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. The two channels of these aqueducts,, one lying on top of the other, can be seen when viewing the cross-section running through the travertine attic at the top of the gate. The gate was incorporated in the Aurelian Wall in 271 by the emperor Aurelian thus truly turning it into an entrance to the city. 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. It was modified further when the emperor Honorius augmented the walls in 405. The foundations of a guardhouse added by Honorius are still visible, while the upper part of the gate, as built by Honorius, has been moved to the left side of the Porta. It is currently known as the Porta Maggiore, possibly designated as such because of the road that runs through the gate leads to the Basilica di Santa Maria Maggiore. The church is an important place of prayer dedicated to the Virgin Mary. 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: TI. CLAUDIUS DRUSI F. CAISAR AUGUSTUS GERMANICUS PONTIF. MAXIM., / TRIBUNICIA POTESTATE XII, COS. V, IMPERATOR XXVII, PATER PATRIAE, / AQUAS CLAUDIAM EX FONTIBUS, QUI VOCABANTUR CAERULEUS ET CURTIUS A MILLIARIO XXXXV, / ITEM ANIENEM NOVAM A MILLIARIO LXII SUA IMPENSA IN URBEM PERDUCENDAS CURAVIT. IMP. CAESAR VESPASIANUS AUGUST. PONTIF. MAX. TRIB. POT. II IMP. VI COS. III DESIG. IIII P. P. / AQUAS CURTIAM ET CAERULEAM PERDUCTAS A DIVO CLAUDIO ET POSTEA INTERMISSAS DILAPSASQUE / PER ANNOS NOVEM SUA IMPENSA URBI RESTITUIT. IMP. T. CAESAR DIVI F. VESPASIANUS AUGUSTUS PONTIFEX MAXIMUS TRIBUNIC. / POTESTATE X IMPERATOR XVII PATER PATRIAE CENSOR COS. VIII / AQUAS CURTIAM ET CAERULEAM PERDUCTAS A DIVO CLAUDIO ET POSTEA / A DIVO VESPASIANO PATRE SUO URBI RESTITUTAS CUM A CAPITE AQUARUM A SOLO VETUSTATE DILAPSAE ESSENT NOVA FORMA REDUCENDAS SUA IMPENSA CURAVIT.
Close by the gate, just outside the wall, is the unusual Tomb of the Baker, built by Marcus Virgilius Eurysaces. In 1917, a subterranean NeopythagoreanPorta Maggiore Basilica was discovered nearby on the Via Praenestina, dating from the 1st century. 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. The vaults are decorated with white stuccoes symbolizing Neopythagorean beliefs, although the precise meaning of elements of the decoration remains a subject of debate.
