The Roman-Byzantine fortress of Carsium was probably built over an already existing Getic fortification, in the second half of the 1st century AD.
At the beginning of the 2nd century AD, during the Dacian wars, in 103 AD, Emperor Trajan strengthened the fortification with stone walls. The proof of this action is an inscription that mentions the fortification works being carried out under the command of an imperial legate of the Praetorian rank, Fabius Postuminus. From this epigraphic source we know that this fortress was raised by soldiers from the 2nd Hispanorum legion. The immediate beneficiaries of the new fortification, however, were the soldiers from “alla gallorum flaviana“, but over the centuries, troops from different legions had stationed in this fort (Legio I Italica, Legio I Iovia Scytica and the Classis Flavia Moesica fleet). For Trajan and the other Roman emperors, Carsium was an extremely important fortress on the river frontier, the mission of the soldiers from here being to defend the river crossing of the Danube. An inscription from Durostorum speaks of the battles of the emperor Aurelianus with the carps which he defeated between Carsium and Sucidava.
The fortress is mentioned frequently in all the documents of antiquity from the 2nd century AD, until the 7th century (Ptolemy, Peutingerian Tabula, Itinerarium Antonini, Notitia Dignitatum, Hierocles, Procopius, Geographer of Ravenna) with the name of Carsum, Carsio, Carso, Carsos. Most likely, the place name has a thracian origin and is related to the rocky appearance of the place. The fortress had the role of ensuring the protection and defense of the most important ford crossing on the Danube, which ensured the connection between the communities in the Romanian Plain and those on the western coast of the Black Sea, and later with the the southern Balkan Peninsula. For the first Christian centuries, evidence point towards a flourishing economic life in the area. Proof to this statement are the architectural elements discovered made out of marble, the large number of discoveries of ceramics artifacts, coins and glass.This was a life comparable to that of the big cities. Unfortunately, events from the Middle Ages and the modern era have largely destroyed these traces. Rural settlements appear near the citadel, some of them appearing rich. There are today, both near Harsova and near Ciobanu, Saraiu and Ghindaresti, the traces of such village settlements.
The outline of the ancient fortification is not yet known. Although it was assumed that the walls on the fortress plateau, which are visible near the Danube, are of Roman origin, recent research refuted this claaim. The constructions are instead of medieval origin, although it is not excluded that some of them were erected at the end of antiquity and then included in the later development of fortifications.
The historical sources indicate the repeated destruction of the fortress and its restoration during the emperors Constantine the Great and Justinian. Older researches, but also recent ones, have discovered archaeological materials of great scientific value both in the fortification and in its necropolis.