Let me say up front that I am not, nor have I ever been—in this life, anyway—an initiate of the Mysteries of Mithras. What follows, therefore, is entirely conjectural.

I am, nevertheless, an experienced New Pagan ritualist who has been through a few ritual initiations himself.

In the absence of evidence, scholars of Mithraism have mostly refrained from attempting to recreate the ancient rites of initiation.

I, however, am not so constrained.

Here's what we know.

Ancient Mithraism was an initiatory path consisting of seven grades—degrees, one could say—each of which corresponded to one of the seven planets of the Ptolemaic universe.

Given, then, what we know about Mithraea—surprisingly uniform across the Roman world—with their church-like layout—narthex (entryway), central aisle, and altar-in-the-front—this is how I would do it.

The Rites of Mithras

Initiation 1°-7°

Opening Rites

Candidate waits (naked?) in narthex during preliminaries.

Opening of the Gate

Door is opened.

In the person of the speleum's Pater Patrorum (“father of fathers”: i.e. high priest), Mithras takes candidate's hand, brings him into the mithraeum, and leads him down the aisle into the presence of the presiding deity of the rite, the masked and robed planetary god—played by one of the brothers—who presides over the current grade of initiation.

The Charge

The planetary god speaks in proprio persona.

The Ordeal

This would have differed with each grade.

The Initiation

This, also, would likely have differed with each grade.

The Oath

Initiate swears an oath of secrecy.

The Presentation

Newly-initiated (or -elevated) initiate is formally presented (by Mithras?) to the assembled brothers.

Applause.

Love Feast

The newly-initiated takes his new place among the brothers.

The typical convivial love-feast ensues.