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 Broch of Clickimin is a large and well preserved, though somewhat restored broch near Lerwick. Originally built on an island in Clickimin Loch (now increased in size by silting and drainage), it was approached by a stone causeway. The water-level in the loch was reduced in 1874, leaving the broch high and dry. The broch is situated within a walled enclosure and, unusually for brochs, features a large 'blockhouse' between the opening in the enclosure and the broch itself. Another unusual feature is a stone slab featuring sculptured footprints, located in the causeway which approached the site. Situated across the loch is the Clickimin Leisure Centre.