The town was founded thousands of years ago probably on account of its hot springs. Some pre-historic remains have been found in what is now the town centre. Later, it became a Thracian city and, when Thrace fell to the Romans and became a Roman province, Hisarya became a Roman town — one of the three most important towns in the province. At times it was called Augusta, Diocletianopolis (after emperor Diocletian), and a couple of other names. It was a famous resort even in those times, which is proved by the fact that emperor Septimius Severus visited the city.
Source: Wikipedia
