Hisarya (Bulgarian: Хисаря, also known as Hisar, Hissar or Hissarya, formerly: Toplitsa, Latin: Diocletianopolis or Augusta) is a small resort town in Bulgaria, in Plovdiv Province.
It is notable for the impressive remains of the ancient Roman city of Diocletianopolis, the enormous walls of which still stand close to their original height for the majority of their circuit. The ancient city lies largely unencumbered by the adjacent modern town, in green parkland full of birdsong. In the centre of the park are still over two dozen hot mineral springs.
In the city have 22 mineral springs, 16 natural and 6 deeply drilled.