A colony of the metropolis of Me-ssem-bria was founded here in 5th century BC. The town was called Anhialo being at the same time a colony of Apolonia as well (today’s Sozopol). The town gradually worsened its relations with Messembria because the population of the latter was Doric in origin and the town was inhabited by the Ionic. The main occupation was fishing, mining and trading of sea salt. The shallow firth presented ideal conditions for that - it was where the first settlers discovered layers of salt in the sand. The ancient town was situated further inward onto the land in the area called Paleokastro where one can see its ruins scattered all over. During the Roman domination Ulpia was added to the name of the town and it surpassed even Apolonia in its glory for a long time. Anhialo regained its name in the Middle Ages. It suffered barbarian invasions and in 8th century it was re-built by the Byzantine empress Irina. The town was intermittently under Bulgarian and then Byzantine domination, and vice versa, but more often in the Bulgarian territory. In 1366 it was conquered and resold to Byzanti-um by Amadeus of Savoy and his knights. It fell under Ottoman rule together with Nessebur in 1453.
At the time of the Kantakouzins family, successors of the last Byzantine emperors, the town became restive again; however Mihail - successor of the family had to escape to Romania. His plan did not succeed and he was hanged, but his sons managed to escape. After the Liberation the town regained its power and was of utmost importance in the Bourgas Bay. In 1906 the town burst in fire and nearly burnt down. It is known as a salt-mining centre; fruits and vegetables grow here; wine and tin productions are traditional for the place. Today the main occupation of its inhabitants is tourism; there is a mud-cure establishment. The mud-cure lake was discovered in 3rd–4th centuries BC and was later called the Holy Lake by Anna Komnina (a Byzantine female writer). The first mud-cure establishment was built here in 1902 after the curing properties of mud unique for Europe had been proved. The mud is good for bone and muscular disorders, radiculitis, rheumatism, sciatica, lumbago, discal hernia, etc.