Across from the village of Ano Vlasia, lies Ancient Leontio, a city of great strategic importance for the interests of the Achaean League, as it was built right on the border of Achaia and Arcadia. Ancient Leontion flourished particularly in the 4th century BC, but although it was fortified with walls and towers, it was destroyed at the end of the 3rd century BC by the Macedonian King Philip V. For many years archaeologists searched for Leontion in the southern foothills of Panachaikos. In 1958, however, a brief excavation on Kastritsi Hill revealed the theatre's cave, located on the northeastern slope of the hill, within the walls of the ancient city.

It was an ancient city of Achaia founded by the Ionians. It was destroyed at the end of the 3rd century BC by Philip V of Macedonia. Today, walls from the acropolis of the ancient city have been excavated on a hill three kilometres northwest of Vlasia and an ancient theatre on the eastern slope of the hill. In present-day Leontio, located 26km north of Vlasia, a temple of Artemis has been found, believed to have been on the ancient road leading to Arcadia.

W.M. Leake identified the ruins of the Kastritsi hill, located 3km from the monastery of Vlasia, with those of ancient Tritheia, while he placed the Achaean city of Leontio in the present-day village of Leontio (former name: Gourzoumisa). His opinion was considered correct for many years, until A. Wilhelm supported the view that ancient Tritia or Tritaia was located in Agia Marina Tritaia, a view later confirmed by P. Nerantzoulis. The Greek historian Polybius includes Leontius among the first twelve Achaean cities, as well as among the ten that still existed in his time. On Kastritsi Hill, a fortified enclosure, the towers and the eastern gate are preserved. In 1958, N. Gialouris excavated the theatre, located within the walls to the north-east of the hill, whose passages and nine rows of seats are preserved. The foundations of houses and other buildings are visible all over the hill.

Theatre

The hollow of the theatre was discovered in 1958 by N. Gialouris during excavations. Today, nine rows of seats have been uncovered, a relic of the fortifications and towers of the citadel, as well as the ruins of three large buildings. The theatre's walkways are preserved at a height of two metres, while from the stone seats of the theatre, the ancient Leontians could see the splendour of the Achaean nature, the fir forests of Erymanthos and the valley of Selinounta.