Boryza's precise location remains unknown and the date of its foundation is debated; it was either founded before or during Darius's European Scythian campaign.[2]
Vassileva, Maya (2015). "Persia". In Valeva, Julia; Nankov, Emil; Graniger, Denver (eds.). A Companion to Ancient Thrace. John Wiley & Sons, Inc. ISBN9781444351040.
Further reading
Izdimirski, Miroslav (2015). Panov, Ivo; Pourmohammad, Alireza (eds.). "Boryza - a Persian polis in Ancient Thrace". Proceedings of International Conference: Iran and Bulgaria in the Mirror of History (Past, Present, Future) (in Bulgarian).