Roman mythology is the set of beliefs, rituals, and other observances concerning the supernatural held or practiced by the ancient Romans from early periods until Christianity finally completely supplanted the native religions of the Roman Empire.
The original religion of the early Romans was so modified by the addition of numerous and conflicting beliefs in later times, and by the assimilation of a vast amount of Greek mythology, that it cannot be reconstructed precisely. Because extensive changes in the religion had already taken place before the literary tradition began, its origins were in most cases unknown to the early Roman writers on religion, such as the 1st century BC scholar Marcus Terentius Varro. Other classical writers, such as the poet Ovid in his Fasti (Calendar), were strongly influenced by Hellenistic models, and in their works they frequently employed Greek beliefs to fill gaps in the Roman tradition.
The Roman ritual practice of the official priesthoods clearly distinguishes two classes of gods, the di indigetes and the de novensides or novensiles. The indigetes were the original gods of the Roman state (see List of Di Indigetes), and their names and nature are indicated by the titles of the earliest priests and by the fixed festivals of the calendar; 30 such gods were honored with special festivals. The novensides were later divinities whose cults were introduced to the city in the historical period, usually at a known date and in response to a specific crisis or felt need. Early Roman divinities included, in addition to the di indigetes, a host of so-called specialist gods whose names were invoked in the carrying out of various activities, such as harvesting. Fragments of old ritual accompanying such acts as plowing or sowing reveal that at every stage of the operation a separate deity was invoked, the name of each deity being regularly derived from the verb for the operation. Such divinities may be grouped under the general term of attendant, or auxiliary, gods, who were invoked along with the greater deities. Early Roman cult was not so much a polytheism as a polydemonism: the worshipers' concepts of the invoked beings consisted of little more than their names and functions, and the being's numen, or "power", manifested itself in highly specialized ways.
The character of the indigetes and their festivals show that the early Romans were not only members of an agricultural community but also were fond of fighting and much engaged in war. The gods represented distinctly the practical needs of daily life, as felt by the Roman community to which they belonged. They were scrupulously accorded the rites and offerings considered proper. Thus, Janus and Vesta guarded the door and hearth, the Lares protected the field and house, Pales the pasture, Saturn the sowing, Ceres the growth of the grain, Pomona the fruit, and Consus and Ops the harvest. Even the majestic Jupiter, the ruler of the gods, was honored for the aid his rains might give to the farms and vineyards. In his more encompassing character he was considered, through his weapon of lightning, the director of human activity and, by his widespread domain, the protector of the Romans in their military activities beyond the borders of their own community. Prominent in early times were the gods Mars and Quirinus, who were often identified with each other. Mars was a god of young men and their activities, especially war; he was honored in March and October. Quirinus is thought by modern scholars to have been the patron of the armed community in time of peace.
At the head of the earliest pantheon were the triad Jupiter, Mars, and Quirinus (whose three priests, or flamens, were of the highest order), and Janus and Vesta. These gods in early times had little individuality, and their personal histories lacked marriages and genealogies. Unlike the gods of the Greeks, they were not considered to function in the manner of mortals, and thus not many accounts of their activities exist. This older worship was associated with Numa Pompilius, the second king of Rome, who was believed to have had as his consort and adviser the Roman goddess of fountains and childbirth, Egeria, who is often identified as a nymph in later literary sources. New elements were added at a relatively early date, however. To the royal house of the Tarquins was ascribed by legend the establishment of the great Capitoline triad, Jupiter, Juno, and Minerva, which assumed the supreme place in Roman religion. Other additions were the worship of Diana on the Aventine Hill and the introduction of the Sibylline books, prophecies of world history, which, according to legend, were purchased by Tarquin in the late 6th century BC from the Cumaean Sibyl.
The absorption of neighboring local gods took place as the Roman state conquered the surrounding territory. The Romans commonly granted the local gods of the conquered territory the same honors as the earlier gods who had been regarded as peculiar to the Roman state. In many instances the newly acquired deities were formally invited to take up their abode in new sanctuaries at Rome. In 203 BCE, the cult object embodying Cybele was removed from Phrygian Pessinos and ceremoniously welcomed to Rome. Moreover, the growth of the city attracted foreigners, who were allowed to continue the worship of their own gods. In this way Mithra came to Rome and his popularity in the legions spread his cult as far afield as Britain. In addition to Castor and Pollux, the conquered settlements in Italy seem to have contributed to the Roman pantheon Diana, Minerva, Hercules, Venus, and other deities of lesser rank, some of whom were Italic divinities, others originally derived from the Greek culture of Magna Graecia. The important Roman deities were eventually identified with the more anthropomorphic Greek gods and goddesses, and assumed many of their attributes and myths.
It is instead only an allegory, rhetorically representing the symbolic personification of the State, first appeared in Rome (269 BC) on coins (nummus), just like in Locri (Calabria) in 204 BC. External peoples might have given Roma divine attributes, but this is only an hypothesis. Emphasising this allegory, temples were erected in Smirne (195 BC) and some sort of cult is reported in Ephesus, Sardi and Delo. A confusion might also be caused by the divinity of emperor: being Augustus a sort of demi-god, what was dedicated to him was a kind of religious celebration, partially directed on town's personality.
Under the empire, the Saturnalia was celebrated for seven days, from December 17 to December 23, during the period in which the winter solstice occurred. All business was suspended, slaves were given temporary freedom, gifts were exchanged, and merriment prevailed. The Lupercalia was an ancient festival originally honoring Lupercus, a pastoral god of the Italians. The festival was celebrated on February 15 at the cave of the Lupercal on the Palatine Hill, where the legendary founders of Rome, the twins Romulus and Remus, were supposed to have been nursed by a wolf. Among the Roman legends connected with them is that of Faustulus, a shepherd who was supposed to have discovered the twins in the wolf's den and to have taken them to his home, in which they were brought up by his wife, Acca Larentia. See founding of Rome.
The Equiria, a festival in honor of Mars, was celebrated on February 27and March 14, traditionally the time of year when new military campaigns were prepared. Horse races in the Campus Martius notably marked the celebration.
The Secular Games, which included both athletic spectacles and sacrifices, were held at irregular intervals, traditionally once only in about every century, to mark the beginning of a new saeculum, or "era". They were supposed to be held when the last person who had witnessed the previous Secular Games died, marking the beginning of a new era. The tradition, often neglected, was revived as a spectacle by Augustus and honored by the poet Horace with a series of odes.
A thorough reform and restoration of the old system was carried out by Emperor Augustus, who himself became a member of all the priestly orders. Even though the earlier ritual had little to do with morality, being mainly a businesslike relation with unseen powers in which humans paid proper service to the gods and were rewarded by security, it had promoted piety and religious discipline and thus was fostered by Augustus as a safeguard against internal disorder. During this period the legend of the founding of Rome by the Trojan hero Aeneas became prominent because of the publication of Virgil's Aeneid.
In spite of the reforms instituted by Augustus, the Roman religion in the empire tended more and more to center on the imperial house, and eventually the emperors were deified after death. Such deification began even before the establishment of the empire, with Julius Caesar. The emperors Augustus, Claudius, Vespasian, and Titus were also deified, and after the reign (AD 96-98) of Marcus Cocceius Nerva, few emperors failed to receive this distinction.
Under the empire, numerous foreign cults grew popular and were widely extended, such as the worship of the Egyptian goddess Isis and that of the Persian god Mithras, which was similar to Christianity in some respects. Despite persecutions extending from the reign of Nero to that of Diocletian, Christianity steadily gained converts, and it became an officially supported religion in the Roman state under Constantine I, who ruled as sole emperor from AD 324 to 337. All the pagan cults were prohibited in AD 392 by an edict of Emperor Theodosius I.