Known as "Olo(Ὀλο[οσσών) in antiquity, in the early Byzantine period it was known as "Lossonos", and was one of the sites refortified under Justinian I (). the modern name first appears in the writings of the 12th-century scholar and archbishop Eustathius of Thessalonica, who considered it "barbaric". At the turn of the 14th century, the Panagia Olympiotissa Monastery was founded on the hilltop citadel. In 1304, Guy II de la Roche, Duke of Athens, passed through during a campaign against the Despotate of Epirus.