The Neo-Mercurians
Our second mystery cult are the Neo-Mercurians. This reconstructionist cult endeavours to recreate the ancient Cult of Mercury. Eschewing the "inventions" (in their words) of Priamitus, they practice only what they believe to be accurate reconstructions of historical Mercurian beliefs and magics. They view their ultimate purpose to be the rediscovery and preservation of Roman culture and magic, a "pure" magic which they view as a boon not just for the initiated, but for all magi.
In the following posts for the Neo-Mercurians we'll have three Neo-Mercurian priests (mystagogues). As these priests tend to a single temple and have a fixed location they are written to cover as broad an area as possible: one is a celtic convert who can be used in otherwise awkward tribunals like Hibernia or Loch Leglean, one can be located anywhere there is an urban temple (hidden in a regio perhaps), and the third anywhere there is a strong magical aura.
Following this are example initiation rites for each mystery the cult commonly initiates. Unlike many cults these have no particular order and are are mainly lacking in ordeals (a single major flaw may be acquired, depending on the order of initiations). They instead emphasise service to the cult, good character, and ability. An initiate who intends to complete the full range and join the ranks of the priesthood can expect to spend decades proving their worth.
In addition an ungifted group of servants who maintain the cult's knowledge of divination, the Quindecimviri are described, with an example grog provided from them. Lastly a set of story seeds and location ideas are given to help use the Neo-Mercurians in your saga.