CIMRM 511 - Inscription by the priest of the Mithraeum at the Domus Augustana. Vatican Museum, Rome.
I.e. To the spirits of the dead, L. Septimius, freedman of the three emperors, father and priest of unconquered Mithras at the imperial palace, made this for himself and for Cosia Primitiva, his well-deserving spouse and their free boy and girl children.
(By the "three emperors" should be understood as Severus, and his sons Antoninus (Caracalla), and Geta.)
According to Adrian van Heck1 this item is now in the Vatican museum.