The administration of the Roman customs and tax system had undergone considerable change under the reign of Marcus Aurelius. The name and career of Caius Antonius Rufus survived in Pannonia, a certainly active participant in this transformation, who directed the custom collection in the territory of the publicum portorium Illyrici, when the modification took place. However, the details of the event, which can be documented with specific names and offices, somewhat differ from the picture laid forth by the scientific literature on the Roman tax system. The change in the system of the custom stations did not happen suddenly, instead the new organisation evolved through several years. Caius Antonius Rufus as the official heading the publicum portorium Illyrici had begun his operations as a conductor, but on the inscriptions dating from the time of Marcus Aurelius he was named as a procurator. During this time the staff of the customs station had not changed, the previous conductor had kept his experienced personnel, who remained his slaves. The complete transformation of the customs station organisation was a longer process, the replacement of the staff with imperial slaves could only have been undertaken little by little on the territory of the publicum portorium Illyrici, not abruptly with the first appearance of the procurator title.