Carsulae is an archaeological site in the region of Umbria in central Italy. It is located approximately 4 kilometres (2.5 mi) north of San Gemini, a small comune in the province of Terni.
 Most historians fix the town's foundation about 220-219 BC. with the building of the ancient Roman road, the via Flaminia. Given the pattern of pre-Roman settlements in the area it is possible that some form of earlier Umbrian settlement existed at this site.
 When the via Flaminia was first built, its western branch proceeded north from Narni (ancient Narnia), sparking the development not only of Carsulae, but also of other locations including  Bevagna (ancient Mevania). This branch of the road courses through a gently rolling upland plain at the foot of the Martani mountain range, an area that had been heavily populated since the middle of the Bronze Age. The  original course of the via Flaminia, the western branch proceeded from Narni past modern San Gemini, Carsulae, modern Acquasparta, the Vicus Martis Tudertium (near Massa Martana), Bevagna and Foligno (ancient Fulginiae). The later eastern branch proceeded from Narni to Terni (ancient Interamna Nahars), north to Spoleto (ancient Spoletium), then past Trevi and finally to Foligno.
 
During the age of Emperor Augustus, Carsulae became a Roman municipium. During his reign a number of major works were initiated, eventually including the amphitheater, most of the forum, and the marble-clad Arch of Trajan (now called the Arco di San Damiano). During its "golden age" Carsulae, supported by agricultural activity in the surrounding area, was prosperous and wealthy. Its bucolic setting, its large complex of mineralized thermal baths, theaters, temples and other public amenities, attracted wealthy and even middle class "tourists" from Rome. While many of the other mentioned towns and cities on the two branches of the old Roman road continue to exist, nothing but ruins remains of Carsulae, which was abandoned and never resettled. In the early Middle Ages, from the 4th or 12th century there is evidence that a small settlement continued,  for example the church of San Damiano that still stands today, was built for a small community of nuns on the foundations of an earlier Roman building.
 For centuries Carsulae was mostly used as a quarry for building materials by nearby towns like San Gemini, Acquasparta, Massa Martana, Terni, and Cesi, where Roman tombstones may be seen built into the former church of S. Andrea. In this period Carsuale reverts to agricultural use without the construction of any major buildings. Recently archaeologists have been able to map the city with considerable detail without the hindrance of more recent structures overlaying the ancient city.
 No one knows the precise reasons why Carsulae was abandoned, but there are four reasons that seem plausible a) that it was destroyed and the site made inhospitable by an earthquake (however, most viable cities hit by earthquakes are rebuilt), b) that it lost its importance and becomes increasingly impoverished because most of the north–south traffic used East branch of the Via Flaminia (Terni, Spoleto, Foligno), c) Carsuale was built in a valley without defensive walls, in the early Middle Ages people tend to move to better defended settlements due to  the political instability that sets in. J.B. Ward-Perkins suggested another effect of increasingly unsettled third century, when the very trunk roads that had been economic lifelines became access roads for hordes of marauders: "Henceforth the tendency must have been to move away from the roads, until by the Middle Ages the roads themselves were as bare of settlement as they had been when they were first built.", d) In the 6th - 8th Century during the period of the "Longobard Corridor" the Western branch of the Via Flaminia is blocked by a conflictual  border between the Imperial Territory and the Duchy of Spoleto, In this period most north–south traffic moves to the West along the Via Amerina.
 Haphazard excavations took place in the 16th century under the direction of Duke Federico Cesi, who sought decorative elements for his palace in Acquasparta. In the 17th century under the Pope Pius VI the first systematic excavations were started in 1783 under Count Sebastiano Graziani of Terni, A. J. Milli in 1800 makes a list of finds discovered in Carsulae during those excavations. [2]
 In 1951, the ruins came under modern methodical archaeological exploration by then "soprintendente" to archaeological heritage for Umbria, Umberto Ciotti. Significant additional work was also done in 1972. The work of U. Ciotti in Carsulae has  been documented in the  publication of an article Carsuale by Uberto Ciotti in San Gemini e Carsulae, Bestetti 1976  and more recently Carsulae I . Gli scavi di Umberto Ciotti a cura di Paolo Bruschetti, Luca Donnini, Massimiliano Gasperini 
 In 2004, after a thirty-year pause in excavation, under the supervision of inspector Paolo Bruschetti, a new excavation campaign was reopened at the Roman Baths directed by Prof. Jane Whitehead of Valdosta State University with the collaboration of the Associazione per la Valorizzazione del Patrimonio Storico San Gemini. In 2020 Prof. Elizabeth Colantoni of the University of Rochester is expected to resume the excavations at the baths taking over the work started by Prof. Jane Whitehead, who retired in 2018.
 
The on-going Italian excavation at Carsulae is led by Massimiliano Gasperini and Luca Donnini. (As of August 2012)
 8:30 to 19:30 from April to September (summer period of validity DST)
(The ticket office closes at 19.00)
 8:30 to 17:30 from October to March (winter period of validity of the daytime)
(The ticket office closes at 17.00)
 Closed on Christmas Day, 1 January and 1 May
 Ticket price: €5.00
 Discounted ticket: €3.50 (EU citizens between 18 and 25 years, teachers with permanent contracts in state schools and tourist groups over 15 paying units.)
 Facilities: Visitor centre with disabled access, "Umberto Ciotti" Visit and Documentation Centre, car parking and café.42°38′23.25″N 12°33′25.75″E﻿ / ﻿42.6397917°N 12.5571528°E﻿ / 42.6397917; 12.5571528
 Video on YouTube with 3D reconstruction of Carsulae.