The region of Aetolia is the southern continuation of the Pindus mountain range, and is bordered on the west by the Acheloos River, and on the east by Mount Oxya. The mountains of Aetolia have peaks exceeding 1818 m, which cut off the rich plains of central Aetolia from the Corinthian Gulf. The south coast of Aetolia between the mouths of the Acheloos and the Euenus rivers has many shallow lagoons, but no serviceable harbor. The only good harbour in Aetolia is at Naupaktos on the Corinthian Gulf, opposite Patrai in the Peloponnese.
There are five cities of importance in Aetolia. Two of these are Kalydon and Pleuron, and Thermon near lake Trichonis, the religious center of Classical Aetolia. Owing to its seclusion from the sea, Aetolia remained undeveloped and knew little urban advancement until the fourth century B.C. Small tribes, however, did form to present a common front against the invasion of Demosthenes in 426 B.C. Only after 370 B.C., with the formation of the Aetolian Confederacy, did this region rise to power and emerge as a close-knit federal state. The natural avenues of expansion for Aetolia lay east in Akarnania and northwards into Malis and Amphilochia, but Aetolia did not explore these possibilities until well into the third century B.C.
Arta in the north was at one time the chief town of the district of Epirus. The town is situated on the left bank of the Arakhthos River and occupies the site of ancient Ambracia, which gave the Ambracian Gulf its name. Founded in the seventh century B.C. by settlers from Corinth, Ambracia became the capital of Epirus under the rule of Pyrrhos, king of the Molossians. In 31 B.C. the people of the town were moved to the newly founded city of Nikopolis.
Thermon, situated on Lake Tichonis in central Aetolia, sits on a natural height commanding the central plains. The city was the spiritual center of the region and was the site of an annual festival during which magistrates were elected. Since the Bronze Age, Aetolia has been a cult center for the worship of Apollo Thermios, Apollo Lyseuis, and Artemis. Over time, Thermon became a Pan-Aetolian sanctuary dedicated to the worship of Apollo Thermios. Remains of successive wooden and stone temples to Apollo Thermios at Thermon are among the oldest religious structures in Greece.
Ancient Pleuron, located to the southwest of Thermon, was known as the city of the Curetes. It was destroyed by Demetrios II, son of Antigonus
Gonatas, in 234 B.C. Pleuron has a remarkable 15 course Hellenistic wall that includes 36 towers and seven gates. Within these walls lay a small theater, a large cistern, an agora, and an acropolis to the north.
Kalydon, southeast of Pleuron, was celebrated in the heroic age as the home of Oineus and his sons Tydeus and Meleager. The famed Kalydonian boar hunt took place on the nearby slopes which culminate in Mount Zygos (944 m). The site consisted of a walled town, a Heroon, and the Sanctuary of Artemis Laphria which stood on a natural spur of land, with a view of the plain and the gulf. On this platform stood a fourth century temple supported by a sixth century retaining wall.
The ancient port town of Naupaktos once belonged to Western Locris, but was captured by Athens in 455 B.C. and used to house Messenians who had abandoned their homes because of the Spartan raids. After the Spartans expelled the Messenians from Naupaktos in 399 B.C., Achaia colonized the town and held it until Philip II captured it and and bequeathed it to Aetolia in 338 B.C. When the Aetolian Confederacy collapsed in 189 B.C., Naupaktos lost its importance.