Aqua Claudia was an ancient Roman aqueduct that was begun by Emperor Caligula in 38 AD and finished by Emperor Claudius in 52 AD.
The total length was approximately 69 kilometres, most of which was underground. The flow was about 190,000 cubic metres in 24 hours. Directly after its filtering tank, near the seventh mile of the Via Latina, it finally emerged onto arches, which increase in height as the ground falls toward the city, reaching over 30 metres.
Nero extended the aqueduct with the Arcus Neroniani to the Caelian hill and Domitian further extended it to the Palatine after which the Aqua Claudia could provide all 14 Roman districts with water. The section on the Caelian hilll was called arcus Caelimontani.
The aqueduct went through at least two major repairs. Tacitus suggests that the aqueduct was in use by AD 47. An inscription from Vespasian suggests that Aqua Claudia was used for ten years, then failed and was out of use for nine years. The first repair was done by Emperor Vespasian in 71 AD; it was repaired again in 81 AD by Emperor Titus.
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.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.