The authors attempt to interpret the theonym Porobonus or Porus Bonus in the Latin dedication from Olbia IOSPE, I2, 171. The inscription is compared with other dedications to the same deity from the Balkans and to god Casebonus. The origin of the theonym Casebonus is obscure; it can be interpreted both as Celtic and Thracian, but adaptation of the Latin Casus Bonus may not be excluded. There are no grounds for interpreting the second theonym as Celtic, it is more plausible to interpret it as the Latin Porus Bonus. The author of the inscription cannot be proved to have been a Celt or a Celtiberian; apparently, he had come from the Low Danube area and was a member of the Roman garrison in Olbia.