Hisarya, Bulgaria

Hisarya is a spa town in Plovdiv Province, Bulgaria, inhabited for approximately 6,000 years thanks to its 22 natural mineral hot springs. By the 5th century BC a Thracian town occupied the site under the Odrysian Kingdom. After Roman annexation around 45 AD, it was renamed Augusta and became one of the most important cities in the province of Thracia. Emperor Diocletian visited in 293 AD and renamed it Diocletianopolis. In the 4th century, massive fortification walls stretching 2.3 km were built against Gothic threats, reaching up to 13 metres high -- among the best-preserved Roman walls in Eastern Europe. The city declined and was largely abandoned by the 7th century.