Sostra is an ancient Roman fort and settlement near the village of Lomets, Bulgaria.Impressive remains have been excavated and partially restored.Sostra was strategically situated along the major Roman road linking ancient Philippopolis and Diocletianopolis in the Roman province of Thrace with the Roman outposts on the Limes Moesiae on the Danube such as Ulpia Oescus and Novae via the Troyan Pass in the Balkan Mountains.The road was vital in Trajan's Dacian Wars against the Thracian tribes north of the Danube, and later became more important as a main artery of the province.
The museum in Troyan contains several finds from the site.
Wikipedia https://en.wikipedia.org/wiki/Sostra
Address (Unnamed Road), Ломец 5669, Bulgaria
Coordinates 42°59'6.053" N 24°40'24.13" E