In the Roman period, from the third century BC onwards, as many as seven of Rome’s aqueducts entered the city from the Porta Maggiore area. This is the highest point in the south-eastern sector of the city, an ideal place from which to channel the waters from the Alban hills and the valley of the River Aniene towards Rome. From here the conduits of the various aqueducts branched out like a fan to reach all parts of the city, following two main routes that ensured the most suitable slope for the water. For centuries, the new conduits overlapped with one another along the same routes. To the west they reached the Caelian Hill and thence the Palatine; to the north, they ran to the area around Termini station, from where the water was redistributed to the Esquiline, the Viminal and the Quirinal hills.

A favoured route for the aqueducts was northwards along the path that, centuries later, was also used by the Aurelian Walls. The first aqueduct to follow this path was the Anio Vetus, built in AD 272 to carry into the city the waters of the River Aniene, from which it takes its name. After entering the city at Porta Maggiore, the conduit continued along a mainly underground route ending at the Esquiline Gate. The water carried by the Anio Vetus was always somewhat murky, so when a number of other aqueducts came into service, it was decided to use its water only to irrigate gardens and for “sordidiora ministeria”: more humble purposes, in other words to clean the sewers. The Aqua Marcia, dating to the mid-second century BC, followed the same path as the Anio but was built almost entirely on piers in opus quadratum. Built on top of it in 125 BC was the Aqua Tepula, named for the “warm” temperature of its water, about 16 degrees at the spring; as a consequence, it was less highly regarded than others. Almost a century after its construction, Agrippa, the son-in-law of Augustus, improved its quality by mixing the waters with that of other aqueducts along the way. Finally, a few years later, the same route was followed by the Aqua Iulia, also built by Agrippa in 33 BC. The overlapping conduits can still be seen at Porta Tiburtina, the arch constructed by the Emperor Augustus in the late first century BC to monumentalize the passage of the aquae over the Via Tiburtina. Later on, the emperors Titus (AD 79) and Caracalla (AD 212) had inscriptions carved on the same gate celebrating the restoration work they had funded.

Today it is even easier to follow the path of the other route, running westwards: Porta Maggiore itself was built where the Aqua Claudia and the Anio Novus crossed the Via Labicana and Via Prenestina roads. The construction of the two aqueducts was begun by Caligula in AD 38 and completed by Claudius 14 years later. Along the present-day Via di Santa Croce in Gerusalemme we still see a stretch of a secondary branch, built by Nero during the construction of his Domus Aurea: the Arcus Neroniani, perfectly preserved thanks to the many restorations of the Imperial period and the Middle Ages.