Roman soldiers had a secret society and we still don't know what they believed. The cult of Mithras. It ran for roughly three hundred years, from the Euphrates to Hadrian's Wall, and it left behind hundreds of temples and not one page of scripture. They met underground, in small windowless rooms built to feel like caves. Stone benches down both walls, room for about thirty men lying shoulder to shoulder. When a group outgrew the space they didn't expand it, they built another one down the street. The port town of Ostia has around eighteen of them. You joined by rank. Seven of them: Raven, Bridegroom, Soldier, Lion, Persian, Sun Runner, Father. We only know the list because of a mosaic floor at Ostia and a letter written by a man who hated them. Getting in meant ordeals. Frescoes at Capua show initiates naked, blindfolded, hands bound, kneeling in front of a standing figure. The temple at Carrawburgh on Hadrian's Wall has a stone lined pit in the floor, big enough for a man. A ceramic vessel from Mainz shows someone drawing a bow on a kneeling initiate. Tertullian, writing to attack the cult, says the Soldier grade was offered a crown on a sword point and had to push it away and answer that Mithras was his crown. Every single temple had the same image at the far end. Mithras in a Phrygian cap, one knee on a bull, hauling its head back and driving a knife into its neck. A dog and a snake drink the blood. A scorpion grips the bull's genitals. A raven watches from the cloak. Two torchbearers flank him, one torch raised, one pointed down. The same scene in Syria and in Britain, for three hundred years, with tiny variations nobody has cracked. We have no idea what it meant. One theory says the figures are constellations. Another says the whole thing maps the soul's route through the sky. Those are educated guesses. The men who actually knew were sworn to silence and they kept it. They left their names on altars. Centurions, legionaries, customs clerks, freedmen, imperial slaves. Hundreds of inscriptions across the empire and not one woman among them. Then it stops. In the late fourth century temples start turning up smashed, statues decapitated, altars broken and buried face down, doorways sealed. The London temple ended up under a building site. The one at Dura Europos was walled into a rampart when the city fell in 256 and sat in the sand for seventeen centuries. Thousands of men. Three hundred years. An entire empire. Not one of them talked.