In the field of Serbian humanities, it has been previously considered that the place name Arilje (former Arhilje) originates from the name of St. Achillius, bishop of Larissa, also called St. Archillius. But recently, the scientific opinion changed towards that in the original Arilje church were first laying the relics of certain St. Archillius, martyr in Sirmium dioecese of Pannonia, and then there were brought the relics of St. Achillius, bishop of Larissa, which in the end were the only ones laying in the present Arilje church, erected by Serbian king Dragutin. According to that opinion, the place name Arilje (former Arhilje) keeps remembrance not on widely known St. Achillius, but on almost unknown St. Archillius, for which nor historical sources, nor folk transmission remembers his relics were ever laying in the Arilje church. Plus, there is an intent to demonstrate the Serbian mediaeval veneration of St. Archillius and it’s mixing with the veneration of St. Achillius in the Serbian church calendar. In this article, however, was given opinion that in Middle Ages name Archillius is the same as the name Achillius, so the place name Arilje (former Arhilje) originates from the name of St. Achillius, bishop of Larissa, also called St. Archillius, as it has been previously considered in the field of Serbian humanities. So, it is about St. Achillius- Archillius, one saint with two name variants. In this article linguistic, as well as extralinguistic argumentation was given to support the above opinion. So, there is no need to generate the idea that in mediaeval Arilje were laying the relics of two different saints with similar names, St. Archillius and Saint Achillius.