Mithras had no mythology that anyone has found. The god who attracted devotees across the Roman Empire for three centuries, whose cult spread particularly among soldiers and merchants, whose underground temples — mithraea — have been excavated from Britain to the Euphrates, left no sacred texts, no founding narrative, no theology explained in its own terms. What we know about the Mithraic mysteries we know from the material record, from hostile Christian commentary, and from scholarly inference — a body of evidence that has produced sustained academic disagreement and no consensus on the most basic questions. Where did the cult come from? What did the central image mean? What happened in the ceremonies? The answers remain genuinely uncertain.

The augurs were among the most important religious officials in Rome, and their function was specific: they observed and interpreted signs — auspices — that indicated whether the gods approved of a proposed action. Before a general led his army into battle, before a magistrate held a public assembly, before a colony was founded or a treaty ratified, the auspices were taken. A favorable sign meant the action could proceed. An unfavorable sign meant it could not — at least not on that day, in that form. The political implications of this system were considerable, and the Romans who operated it were not naive about the opportunities it created.

The Romans buried their dead outside the city. This was law and custom simultaneously — the Twelve Tables prohibited burial within the city limits, and the prohibition was observed with sufficient consistency that the great roads leading out of Rome were lined with tombs for kilometers. The Via Appia’s funerary landscape, stretching from the Porta Capena south through the Alban hills, was among the most concentrated assemblages of monuments to the dead in the ancient world, ranging from the elaborate mausolea of senatorial families to the simple markers of freed slaves and soldiers. Death organized itself along the roads the living traveled, which meant that Romans moved through the presence of their dead every time they left the city.

The Romans were simultaneously the most practically minded people in the ancient world and among the most superstitious. This is not a contradiction. Superstition — the belief that specific acts, objects, words, and encounters have causal effects on outcomes beyond what rational analysis can explain — tends to flourish precisely among people who need reliable outcomes and who have incomplete knowledge of the mechanisms that produce them. The Romans needed reliable harvests, reliable military victories, reliable births, and reliable business outcomes. Their practical knowledge of how to achieve these things was considerable but not complete. The gap between what they knew and what they needed to know was filled by omens, amulets, spells, and the accumulated lore of good luck and bad luck that constituted Roman superstition.

The unconquered sun — Sol Invictus — was the dominant religious force in the Roman Empire during the decades immediately before Christianity became the state religion, and the competition between them was closer than the outcome suggests. Aurelian, who reunified the empire after the chaos of the third century and who is one of the more underrated figures in Roman imperial history, established Sol Invictus as the supreme deity of the Roman state in 274 AD, built a spectacular temple in Rome, and created a new priesthood — the pontifices Solis — to administer its cult. For roughly forty years, the sun god was in a position of official supremacy that Christianity would not achieve until the reign of Theodosius nearly a century later.

In 186 BC, the Roman Senate issued the senatus consultum de Bacchanalibus — the decree concerning the Bacchic rites — one of the most extensive surviving Roman legal documents and the record of what the Roman state did when it decided that a religious movement had gotten out of hand. The decree restricted the Bacchic associations throughout Italy, required their leaders to present themselves for investigation, set numerical limits on how many people could participate in the rites, and prohibited Bacchic priests from holding funds or conducting initiations without specific Senate authorization. Thousands of people were prosecuted; the sources describe executions in numbers that suggest a systematic repression rather than individual criminal cases. The Bacchanalia, as the Roman sources describe it, was the first large-scale persecution of a religious movement in Roman history.

Isis arrived in Rome over official objections. The Roman Senate banned her worship multiple times in the first century BC — in 58, 53, 50, and 48 BC, with varying degrees of enforcement — ordering her altars demolished and her images removed from the city. The bans failed because the cult’s appeal was stronger than the official resistance, and by the first century AD the goddess who had been repeatedly expelled was being worshipped in temples funded by emperors. Caligula built her a major temple in the Campus Martius. Vespasian and Titus celebrated their triumph over Judaea in her temple precinct. Commodus appeared in her processions in priestly dress. Whatever the Senate of the Republic had thought about Egyptian divinities, the Empire had reached different conclusions.

Rome was not original in its theology, and it did not pretend to be. The Romans were systematic borrowers of divine power, operating on the practical assumption that a god who worked was worth incorporating regardless of origin. The result was a pantheon that was Greek at its core, overlaid with indigenous Italian tradition, supplemented by imports from Egypt, Persia, and Syria, and eventually contested and replaced by a monotheism that originated in Judea. Roman religion was an accumulation, not a creation.

The Pantheon is the best-preserved ancient building in the world, and it is better preserved than most medieval buildings, because it has been in continuous use since its construction. Hadrian built it between approximately 118 and 128 AD on the site of earlier temples in the Campus Martius district of Rome, and it has served as a temple, a church, a tomb, and a tourist site across nineteen centuries without the structural interruption of abandonment. The dome that spans its interior has not been surpassed in diameter — 43.3 meters — by any unreinforced concrete construction in the two thousand years since it was poured. Whatever Rome’s engineers knew, they knew something that took a very long time to recover.

The Saturnalia began on December 17 and lasted, in its imperial development, for seven days. It was the most popular festival in the Roman calendar, the one that Roman writers mention most frequently as a cherished institution, and the one whose customs have attracted the most scholarly attention for their relationship to the Christmas traditions that eventually overlapped with and largely replaced them. For the duration of the Saturnalia, Roman social life was deliberately inverted: slaves were served dinner by their masters, social distinctions were relaxed, gambling was legally permitted, gift-giving was universal, and the general atmosphere of licensed excess provided a temporary release from the hierarchical rigidity that organized Roman life during the other fifty weeks of the year.

The Vestal Virgins were the most socially privileged women in Rome and, simultaneously, subject to a punishment for a specific transgression — unchastity — that no other Roman citizen faced: burial alive. The combination of exceptional status and exceptional vulnerability was not a paradox in the Roman religious framework but a logical consequence of what the Vestals were understood to represent. Their virginity was not a personal moral choice; it was a civic necessity. The sacred fire they tended in the Temple of Vesta was, in Roman religious understanding, the eternal flame of Rome itself, and its maintenance by women who were themselves unbreached vessels was what kept Rome’s divine favor intact. When a Vestal was unchaste, it was not a private transgression but a public catastrophe that had to be addressed with proportionate ritual severity.