Two emperors, one project
Caligula started it in the second year of his reign, 38 CE, together with a second aqueduct, the Anio Novus. Claudius completed both on a grand scale and dedicated them on 1 August 52 CE, as Frontinus, the commissioner who ran Rome’s water supply at the end of the century, records. The new aqueduct took his name.
Its water came from two springs, the Caerulean and the Curtian, near the thirty-eighth milestone of the road to Subiaco, in the upper valley of the Aniene east of Rome. From there the channel ran 46,606 Roman paces to the city, about 69 kilometres.
Seventy kilometres, mostly out of sight
Like all of Rome’s aqueducts, the Claudia moved water by gravity alone, along a channel with a very gentle slope. And like them, it kept out of sight wherever it could. Of its 46,606 paces, 36,230 ran underground. The rest, 10,176 paces, ran above ground, and the most spectacular part began at the seventh milestone from the city: 609 paces on substructures and then 6,491 paces, almost ten kilometres, on a line of arches across the plain to the gates.
Why so high? The channel had to keep its gentle slope while the plain dropped towards the city, so the arches grew taller as the ground fell away. On top of the Claudia’s channel ran a second one, carrying the Anio Novus. Two aqueducts shared one set of arches, stacked like a double-decker bus.
A gate that began as an aqueduct
Where the two channels crossed the roads to Praeneste and Labici, Claudius built a monumental double arch in 52 CE. Its attic still carries the inscriptions of Claudius, the builder, and of the emperors who restored the aqueducts, Vespasian in 71 and Titus in 81. Two centuries later the arch became something else. In the 270s the emperor Aurelian built new walls around Rome and used the aqueduct crossing as one of the walls‘ gates. That is Porta Maggiore. Beside it stands the late Republican tomb of the baker Eurysaces and his wife Atinia, and under the arches you can still see the original Roman road.
Rebuilt by a pope
In 1585 Pope Sixtus V built a new aqueduct, the Acqua Felice, and between Via del Mandrione and Porta Maggiore it runs on top of the old line of the Claudia. The Acqua Felice still works. So in a few places, the arches built for Claudius ended up holding water again sixteen centuries later.
Where to see it
The best place is the Parco degli Acquedotti, a public park of about 240 hectares at Via Lemonia on the south-eastern edge of Rome, open from dawn to dusk (Turismo Roma, October 2026). There, 155 piers carry the arches of the Claudia across open fields, next to the later Acqua Felice and the remains of the Aqua Marcia. Porta Maggiore shows where the aqueduct entered the city.
Sources
- Frontinus, De aquis 13-15 (trans. Bennett, LacusCurtius).
- Turismo Roma (Roma Capitale), “Parco degli Acquedotti”; “Porta Maggiore e il Sepolcro di Marco Virgilio Eurisace”; “Piazza di Porta Maggiore”.
- Italia.it, “Porta Maggiore”.
