The article deals with a Roman tombstone discovered in 2008 during the renovation of the façade of the church of St. Peter at Jezero near Trebnje, which mentioned two town magistrates of Celeia, Gaius Longinius Severinus, and his son, Longinius Avitus. The circumstances of the discovery are  described,  as  are  other  worked  Roman  stones  reused in the church wall, the history of the church, the method of  presentation  and  conservation  of  the  monuments,  the results  of  the  geological  analysis  of  the  stones,  and  the geophysical investigation of the site. The description of the monument is followed by a textual analysis and historical commentary.  The  list  of  town  magistrates  of  Celeia,  who were  previously  attested  mostly  on  inscriptions  from  the southern part of the province of Noricum, has thus been supplemented  for  the  first  time  with  this  newly  found inscription from the province of Pannonia