Pirot is 65 km or about 40 miles from the border with Bulgaria. Slavs began to settle in this part of the Roman Empire in the 6th century A.D. 2500 years ago, or 500 B.C., before either the Macedonian or the Roman conquest of this area, the region had Illyrian and Thracian tribes—apparently this locale was in the Thracian area.
Thanks VR.