East Rumelia

 was part of the the Ottoman Empire. In the 1880s there was a revolution which resulted in East Rumelia becoming a part of Bulgaria. Philippopolis and the Bellova Forest were both located there. (AUDIO: The Bellova Devil)

Behind the scenes
While not mentioned in the story itself, East Rumelia was an autonomous Ottoman territory from 1878 to 1885, when it was liberated in a bloodless revolution and became a part of the the Principality of Bulgaria.