The city of Nikopolis was founded following the victory of Gaius Julius Caesar Octavianus (Augustus) in the naval battle of Actium in 31 BC. The city is associated with the effort to establish Roman dominion and the whole process of 'Romanizing' Greece. The province of Nikopolis extended southwards from the mountains of Cassopeia as far as the province of Roman Patra and to the north from the river Acheloos to Leucas (present-day Lefkada). Augustus Caesar granted the city substantial political and economic privileges and adorned it with magnificent monuments while also reviving the Actium Games. The name of the king of Judea, Herod I, and those of many Roman officials such as Germanicus, Nero, Hadrian, among others are associated with donations to Nikopolis. Nikopolis was capital of Epirus and Acarnania during the first three centuries of the Roman Empire. Built at the crossroads of commercial land and sea routes, it was the centre of Greek culture and a meeting point between the eastern and western worlds. It was the seat of Epictetus' school of philosophy while a Jewish community lived within the city. Between the 3rd and 5th century AD the city underwent a period of relative decline and stagnation while from the mid 5th century AD Nikopolis became the administrative, artistic, spiritual and religious centre of the area with a Christian character. According to tradition the church of Nikopolis was founded by the Apostle Paul. During the early Christian period the city experienced a major economic and spiritual boom, a fact demonstrated by the fortification programme instigated by Justinian and from the plethora of monuments which adorned the city. The administrative reorganization of the Byzantine Empire in the 9th century and the transfer of the capital of the Theme of Nikopolis from Nikopolis to Nafpaktos led to the city's decline and abandonment which was completed during the 13th century.
The city with the fortification walls and the cemeteries occupies a fertile strip of land between the Ionian Sea to the west and the Ambracian Gulf to the east, where two of the three city harbors were located. The third harbor ran along both sides of the inlet known as Ormos Vathy at the north edge of the modern city of Preveza. The city occupies an area of approximately 375 acres.
The plan of the city was the rectangular grid with decumanus (the main east-west street) and cardo (main north-south street) intersecting at its center. Nicopolis was planned within walls with four main gates at the compass points. The southern quarters of the city were mainly composed of residential houses but also included the Odeum, while the northern section saw the rise of Augustus monument as well as the construction of the Theater, the Gymnasium and the Stadium. This area known by the ancient writers as the "Suburb", is located outside the roman fortification walls, on the hills with a magnificent view towards the Ionian sea and the Preveza peninsula.
The city had a very effective water supply system. A 50 km long impressive aqueduct, constructed with a series of arches (arcade) and tunnels, carried the water from the Louros springs to the Nymphaeum and it was distributed within the city.
In the early Christian times the size of the city was reduced to almost 1/6 and strong fortification walls, known as the Christian (Byzantine) Walls were built. Two great basilicas and an Episcopal megaron built around this time, reveal that the city flourished during that period.
The most important public buildings are the following:
-The monument of Augustus: It was founded by Octavian in memoriam of the battle at Actium.
-The Theater: The scene is tall, probably two stories high with three arched doorways. The performances took place at a stage panel between the scene and the orchestra. Three corridors allowed the access of the spectators to the auditorium, which was supported by three semicircular porticos.
-The Odeum: It consists of the auditorium, the orchestra and the scene. Three semicircular porticos achieve the inclination of the auditorium. It was built at the 1st cent. AD. and it was in use until the 2nd half of the 3rd cent. AD.
-The Nymphaeum: It lies on the western side of the roman fortification walls, consisting of two pi-shaped brick structures with plain external facades and internal niches. These cisterns stood at the terminus of the aqueduct, which brought water to the city from the Louros springs, 50 km away. Possibly built at the time of Adrian.
-The North thermae: Roman public building. It is situated on the western side of the roman fortification walls. It consists of circular and quadrangular rooms, decorated with niches and arches.
-The Basilicas: Seven Christian basilicas are to be mentioned. Four of them lie within the perimeter of the Byzantine Walls. Basilica Alpha was founded by the Bishop Doumetius (525-575 AD) and it is decorated with elaborated mosaics, combining floral and pictorial motifs. Mosaics are to be found in the Basilica Beta, built at the time of the Bishop Alcison, who was active during the reign of the Emperor Anastasios (491-518 AD). A century later (575-600 AD), another basilica, Basilica Gamma, was built at the northern quarters of the Byzantine fortification while at the south a fourth Basilica, Basilica SigmaTau, was discovered as early as 1981. Two other basilicas - the Ayrmatos Basilica and the Basilica of the Holy Apostles - are situated outside the perimeter of the Byzantine walls.