In 1896 Franz Cumont published, as the second volume of his Textes et monuments figurés relatifs aux mystères de Mithra, the dossier of documents on the basis of which he was to render, three years later, the first truly historical account of the transformation of Mithra-worship from a branch of Iranian Mazdaism to a Roman mystery cult.
This transformative process, as he envisaged it, was long and evolutionary. He used a geological metaphor to describe its stages, as theology and practice were passed down the ages and across the lands from Iran to Rome:
Le fond de cette religion, sa couche inférieure et primordiale, est la foi de l'ancien Iran, d'où elle tire son origine. Au-dessus de ce substratum mazdéen, s'est déposé en Babylonie un sédiment épais de doctrines sémitiques, puis en Asie Mineure les croyances locales y ont ajouté quelques alluvions. Enfin, une végétation touffue d'idées helléniques a grandi sur ce sol fertile, et dérobe en partie à nos recherches sa véritable nature.
Central to Cumont's scenario was Anatolia and the Mazdean diaspora that survived (and flourished) there after the fall of the Achaemenian empire. It was there during the Hellenistic Age that ‘Mithraism received approximately its definitive form’, although Cumont hesitated to pinpoint the precise time and area.