Tomb of Seuthes III (reign c. 331 BC to c. 300 BC.).
See:
- Emil Nankov, Berenike Bids Farewell to Seuthes III: The Silver-Gilt Scallop Shell Pyxis from the Golyama Kosmatka Tumulus in: Archaeologia Bulgarica, XV, 3 (2011), pp. 1-21 - https://www.academia.edu/1541385
- http://www.muzei-kazanlak.org/index.php?option=com_content&view=article&id=72&Itemid=88&lang=en
- Hermann Bengtson: Herrschergestalten des Hellenismus, Beck'sche Sonderausgaben 1984
- Julia Valeva, Emil Nankov, Denver Graninger: A Companion to Ancient Thrace, John Wiley & Sons 2015,different pages