Anchialos (also known as Anchialo, Acheloos, and Achelous) is a historical region that has been mentioned in several ancient texts such as Thucydides' "History of the Peloponnesian War."
Anchialos is located in ancient Thrace, modern-day Bulgaria. It is positioned near the coast of the Black Sea and to the east of the Nestos River. Its exact boundaries have shifted and changed over times, giving rise to several cities and fortresses. Over different eras, it has been dominated by Thracians, Macedonians, Romans, Byzantines, Bulgarians, and Ottomans successively.
The ancient city of Anchialos was reportedly founded by the Thracians and later expanded by the Greeks. It was known as an important trade and military hub. A major highway connecting Byzantium and Mesembria passed through Anchialos, making it strategically important.
The city was renowned for its hot sulphur springs that were believed to have medicinal properties. Roman emperors, such as Septimius Severus and Justinian I, visited the city for its baths. It was also known for its wine production.
In the Byzantine era, Anchialos was noted for its strong fortifications and sturdy walls. Despite this, the city was repeatedly besieged and captured by Slavs, Avars, Arabs, Pechenegs, Varangians, and Crusaders over the centuries.
Nowadays, the remnants of Anchialos can be found near the Bulgarian resort city of Pomorie, which houses several sites of archaeological interest, including a Roman fortress and baths, a prehistoric necropolis, and a Byzantine basilica. However, much of the ancient city remains unexplored.