Aqua Claudia

Aqua Claudia ("the Claudian water") was an ancient Roman aqueduct that, like the Aqua Anio Novus, was begun by Emperor Caligula (37–41 AD) in 38 AD and finished by Emperor Claudius (41–54 AD) in 52 AD^{: 187 : §1.13 (p. 352-355}.

It was the eighth aqueduct to supply Rome and together with Aqua Anio Novus, Aqua Anio Vetus and Aqua Marcia, it is regarded as one of the "four great aqueducts of Rome".

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The aqueduct went through at least two major repairs. Tacitus suggests that the aqueduct was in use by AD 47^{: §11.13 (p. 268-9)}. An inscription from the time of emperor Vespasian suggests that Aqua Claudia was used for ten years, then failed and was out of use for nine years. The first repairs took place during the reign of Vespasian in 71 AD^: 187. The aqueduct was repaired again in 81 AD by emperor Titus^: 187. Additionally, brick stamps from 123 AD testify to some restorations during the rule of emperor Hadrian. Honorary inscriptions from the 5th century show that repairs were done during the rule of Arcadius and the rule of Honorius too^: 188. Later repairs were made by Belisarius during the 6th century, and the pope Adrian I during the 8th century^: 188.

Alexander Severus reinforced the arches of Nero (CIL VI.1259) where they are called arcus Caelimontani, including the line of arches across the valley between the Caelian and the Palatine.

The church of San Tommaso in Formis was later built into the side of the aqueduct.