The ruins of Nikopolis, built in 28 BC by Octavian (later Augustus), after he defeated Mark Antony and Cleopatra in the naval Battle of Actium (Aktion), include Roman walls, Byzantine walls and churches, a stadium and two theatres. Much was destroyed by Bulgarians in the 11th century, but the scale of the ruined 'City of Victory' remains breathtaking, even if it requires a little imagination to conjure. It helps to visit the museum first.
The main site entrance, 5km north of Preveza, leads to a Byzantine church and, a bit north, the Roman odeon. Farther north along the road are long stretches of the walls erected by Emperor Justinian in AD 540. Around another bend is the Roman stadium and a larger theatre, with seating for 5000. These are all by the roadside and accessible for free. Allow a couple of hours to hike the site on foot, if you come by bus (take any bound for Filippiada or Ioannina). With a car you can cover the whole area more quickly, and also follow the signs for the farther-flung 'Actium Trophy', the massive monument Octavian built after the battle. The huge wall here once displayed the battering rams from the conquered warships.
