When it came to religion, the world of the Roman Empire witnessed a mix of old and new, tradition and innovation. In the Archaic and Classical periods, religion had largely been a matter of the community or the state, but in the Hellenistic period at the latest various forms of a more personal religiosity and more private religious organizations blossomed besides the traditional state cults. That development continued during the empire, so that apart from the cults maintained everywhere by the Roman state or by the various cities and provincial councils, private religious organizations and private religiosity flourished.
The traditional cults persisted until well into the 4th century AD. Inscriptions and votive offerings testify to the ongoing worship of Jupiter or Zeus, of Hercules, Apollo, Dionysus, and many other representatives of the classical pantheon. But it is clear that these deities could no longer monopolize the attention of their worshipers, for they were often overshadowed by other divine figures and other cults that promised a more intense contact with their worshippers.
In the Hellenistic period, the need for a more intimate relation between man and deity as well as between the worshippers of one and the same deity themselves had given rise to the spread of various cult associations and the worship of particular deities that seemed to meet that need. Typical of the age was the syncretistic character of many of these gods and cults, where elements of different origin merged into one divine figure or into one complex
Of myths and rituals. Moreover, often the worshipers of Isis, Asclepius, or other deities considered their god the greatest, the mightiest, or the highest. In henotheism, one god or goddess was seen as standing above all others, ruling all the others as his subordinates, or even comprising all the others as aspects of himself. During the empire, private cult associations and the phenomenon of henotheism spread even more widely. That could also be said of the worship of, or at least the anxious reverence for, the divinized powers of Luck or Fortune (Latin: Fortuna) and Fate or Destiny (Latin: Fatum). The latter was often linked with astrology, since the stars and the planets in the opinion of nearly everybody in principle determined the destiny of men and states. At the same time, practically all people attempted to influence gods and planets in order to change their fate. This explains to a large extent the wide diffusion of all sorts of magical practices. In the same category belonged the extraordinary powers that were attributed to certain people: wise or holy persons who had a special relationship with the divine world and were therefore able to perform miracles and overcome the decrees of fate. With these acts, they proved that they had been chosen by a higher power or even that a divine being resided in their human body. Such ideas too had emerged in the Hellenistic period but spread more widely during the empire.
The religious picture of the Roman Empire in the first three centuries can thus be sketched in a few broad strokes. In the first place, local cults proliferated everywhere, which as a result of contact with Greco-Roman culture had often been hellenized or romanized to various degrees. Many Celtic deities, for example, had in the process of interpretatio Romana been identified with gods such as Mercury (Mercurius, Greek Hermes), Apollo, Mars, or Hercules, while in Asia Minor, to mention another example, many local gods and goddesses were identified with the Greek Zeus, Artemis, Aphrodite, and others. This syncretism was a natural part of a wider process of acculturation. In the larger cities of the empire and in the old core lands of Greece and Italy, the traditional deities still possessed their temples and cults paid for by the city or the state.
But besides the traditional cults, various more recent cults of non-Greek or non-Roman origin had appeared, often in the form of private cult associations. Since the Hellenistic period and well into the 3rd and 4th centuries AD Isis and the Anatolian goddess Cybele were extremely popular; since the early empire, it was, among others, the god Mithras, whose cult acquired numerous adherents. The followers of Mithras were mainly found among government officials, officers, and soldiers, and his cult places, Mithraea, along the military roads and adjacent to the camps at the frontiers, as well as in Rome and Ostia. Mithras was a god with a Persian name who in the Roman Empire by a syncretistic process had been assembled from elements of other cults and deities. For instance, he could easily be equated to the sun god. His worship flourished especially during the 3rd century, together with that of Sol Invictus, the Unconquerable Sun, who was then promoted by some of the emperors as the special protector of the empire and of their own persons. At the same time, the cult of Mithras was closely connected with astrology and with the notion of an immortal soul that came from a realm of light beyond the stars where, after death, she would return by ascending through the various spheres of the planets with the help of Mithras, who would protect her against the planet gods.
Such ideas about a journey of the soul to heaven were also known outside the circles of the worshipers of Mithras. They corresponded with the prevailing view of the universe of many intellectuals and with the belief in an immortal but immaterial soul that was held by most philosophers. As far as we know, the large majority of inhabitants of the Roman Empire did not have any strong beliefs regarding the afterlife. The numerous funerary inscriptions testify mostly to a pessimistic resignation: the grave is literally the last resting place, and death the end of life. Some of the deceased, who had not been buried properly, were believed to roam Earth as ghosts haunting the living, but that was not an enviable fate and certainly no solace for their relatives. Some special cults, such as the old mysteries of the goddesses of Earth and the grain at Eleusis in Attica, and also more recent ones such as those of Isis and Mithras, promised some form of existence of the soul after death for their worshipers who had undergone initiation. But we know little more about the messages preached by these so-called mystery cults (from musterion, initiation), since they required their adherents to keep silent about what they heard and saw. Certainly, the notion of an afterlife for the soul was spread by some philosophical schools that based themselves on the teachings of Pythagoras and Plato and had become rather popular during the empire. According to them, human souls originated in a realm of light and pure spirit somewhere between the stars or even beyond; through the spheres of the planets they had invisibly descended on Earth and entered into human bodies (either at conception or at birth); after death, in the vast majority of cases they moved to another body, human or animal, but the souls of those who had disassociated themselves from material greed and immorality and had led an ethically pure life dedicated to philosophical contemplation would ascend again, escape from Earth and find rest in the heaven of their origin. Such ideas lived on among relatively small groups, but they were important because of their influence on Christians and related groups, as well as on the philosophical school of Neoplatonism that was prevalent in late antiquity. In Neoplatonism, Plato’s doctrine of the ultimate reality of ideas was revived in decidedly religious form that tended toward mysticism. Its founder in the 3rd century was Plotinus, who studied in Alexandria and then moved to Rome, where he founded his own school. His followers would dominate the last centuries of pagan philosophy until the final closure of the Platonic Academy in Athens in the 6th century AD.
In the Roman world, belief in miracles, in miracle workers and in “divine” humans was widespread. A “divine” man—or a “human” god—was also the Roman emperor himself. The Hellenistic tradition of the ruler cult had been effortlessly transferred to Octavian/Augustus. After the civil wars had been brought to an end and after the chaos, plundering, and extortions, especially in the east of the empire, a period of reconstruction had begun, and the divine worship that many Greek cities paid to the man who had become sole ruler was largely spontaneous and honest. “Savior” and “Benefactor” were the most common names with which he was addressed; altars, statues, and temples were the material expressions of this cult. In Rome and in Italy, Augustus and most of his successors mitigated this cult somewhat, because an all too official divinization did not sit well with the fiction of the emperor as princeps among his fellow senators, who had restored “the republic” and since then maintained it. But also in Rome, it was clear to everyone that the emperor was not an ordinary human being. After his death
He was officially declared a divus, that is a god, by the senate and was supposed to take his place among the other gods; in Rome, his statue would be placed in a temple of his own or in the temple of another divus or another god, while outside Italy his statues were usually already in his lifetime placed in such sanctuaries. Likewise, various attributes of the emperor and the very name Augustus itself already suggested a near-divine status for the living ruler. Some emperors commended to be given divine honors in Rome as well—for instance, Caligula and Domitian—but because of their despotic rule, the senate in their case refused them posthumous divinization (cursing and erasing their memory, instead). Meanwhile, the cult of the living emperor spread also to the western provinces. Already under Augustus it was organized, closely connected with the cult of the goddess Roma, in the two regional centers Tarragona in Spain and Lugdunum (Lyons) in Gaul. At annual festivals and fairs, sacrifices were brought and games celebrated that together took on the character of a show of loyalty of the provinces to the emperor and to Rome. Comparable provincial organizations of the emperor cult appeared in the east, especially in Asia Minor. There, the office of provincial high priest for the cult of the emperor was much sought after by the local aristocrats. With all that, the emperor cult assumed a clearly political element as an expression of loyalty and solidarity. Still, sincere religious emotions did certainly play a role in this worship of this mighty figure who was so far away in Rome and yet so powerful that he could only be conceived of as a god. Gradually, such ideas spread also in Rome and Italy. When the emperors came to behave more and more as absolute rulers, divinization during their lifetime was accepted in Rome as well. During the troubles of the 3rd century, some of the so-called soldier-emperors tried to make their position unassailable for would-be rebels and pretenders by presenting themselves as the special companions or favorites of a mighty god, usually the Unconquerable Sun, and thus enhancing their own divine status. Some of them called themselves openly “Lord and God” (dominus et deus): some of Aurelian’s coins carried the message “Born Lord and God.”