Around 900 A.D, the Byzantine fleet from Naupaktos (Lepanto) at the Gulf of Corinth became the capital and was named Nikopolis. The new capital became secured by the fortress. One of these fortresses were favourable for defense on the island and the lagoons in Aitoliko. Since the 12th century, the island fortress of Anatoliko developed into a city. In 1406, it was sold to Carlo I Tocco of Kefallinia. The Venetian forces divided their incomes from the salt gardens and fishing waters of Anatoliko which lasted until 1430.

During the Greek War of Independence against the Ottoman Empire, in the beginning of the 19th century, Aitolikon experienced three Turkish sieges before it became a part of Greece. There were 500 Greek defenders and 15,000 Turks in the first siege. The second siege was repelled, and in the third siege, Aitolikon was re-taken by the Turks at the same time as Mesolonghi on April 11, 1826. Generals from Greece that participated included Georgios Liakatas.