Plevrona was one of the major cities of atolia. It is located at the foot of Arakynthos northwest of Messolonghi. Today the locals call these ruins “Castle of Kyra Rini” as well. According to mythology the area was named after Plevronas, son of the founder of Etolia, Etolo.In history it is referred to as Old Plevrona and New Plevrona. Old Plevrona has been completely destroyed since the Dimitraikos war 236 BC - 233 BC by King Dimitrios’ Army, who is also known as Dimitrios the Etolian. New Plevrona was built in 234 BC and developed an important civilization until 30 BC when its inhabitants were taken by the Romans to Nikopolis, in Preveza.
Among the archaeological findings in New Plevrona, the city wall is of great interest, as it is in excellent condition and is built with hewn stone blocks. The wall consists of thirty towers and six gates.
Among the surviving findings of the city, the theater takes pride of place thanks to its innovative stage, which incorporates a section of the wall, a huge water tank, the market (agora) and the cemetery.
Μεταξύ Καλυδώνας και Πλευρώνας, στη θέση «Χίλια Σπίτια», σε απόσταση 1 χλμ. βορειοανατολικά του σημερινού οικισμού του Αγίου Θωμά, βρίσκονται τα ερείπια της αρχαίας πόλης της Αλίκυρνας.