Mithreum of Jajce i Dalmatia was built in the early 4th century AD.
See:
- CIMRM 1901 - Mithraeum. Jajce, Bosnia -http://www.tertullian.org/rpearse/mithras/display.php?page=cimrm1901
- Philippa Adrych, Robert Bracey, Dominic Dalglish, Rachel Wood, Stefanie Lenk, Images of Mithra, Oxford University Press, 2017, p. diff.