Pagan Roman
The Roman state religion was a complex interlocking of cults, temples, and shrines, all in service to the greater glory and spiritual health of the Roman state and people (res publica et populi).

Currently present: Arval Brethren, Flamen Dialis, Flamen Martialis, Flamen Quirinalis, Imperial FlaminesPontifex Maximus, Rex Sacrorum, Virgo Vestalis Maxima,

Fratres Arvales) The Arval Brethren were a body of priests in ancient Rome who offered annual sacrifices to lares and gods to guarantee good harvests. The term can be translated as "Brothers of the fields". The modern world knows them mainly from stone carved records of their oaths, rituals and sacrifices. The priesthood, which dated back to the old Roman kingdom and was probably of Sabine origin, presided over the worship of Dea Dia, a fertility goddess and aspect of Ceres. In May, the Arvales presided over Dea Dia's three-day festival and chanted the Carmen Arvale, a prayer so ancient that its meaning was no longer understood by late Republican times. There were twelve Arvales, normally chosen from patrician families. Each year the Arvales elected officers from among their ranks, including a magister (who presided over the order), a promagister and a Flamen Arvales (who was responsible for the ritual aspects of the order). Of diminished importance by late Republican times, the Arvales were restored to prominence by Augustus.

The Flamen Dialis was an important position in Roman religion. The Flamen Dialis was one of three flamines maiores, the flamines serving the three gods of the Archaic Triad (Jupiter, Mars, and Quirinus). In particular, the Flamen Dialis was the special priest of Jupiter Optimus Maximus (Best and Greatest), Jupiter in his incarnation as chief god of the Roman state. The Flamen Dialis enjoyed many honors. When a vacancy occurred, three patricians, whose parents had been married according to the ceremonies of confarreatio (the strictest form of Roman marriage), were nominated by the Comitia, one of whom was selected and consecrated by the Pontifex Maximus. From that time forward he was emancipated from the control of his father and was, alone of all priests, permitted to wear an apex, be preceded by a lictor, and wear the toga praetexta. He enjoyed automatic membership in the Roman senate by virtue of his office. Only the Rex Sacrificulus or Rex Sacrorum was entitled to recline above him at a banquet, and he had the power to free fugitive slaves who took refuge in his house and grant respites to condemned criminals who fell suppliant at his feet. The Flamen Dialis was also subjected to a an extensive list of taboos, including prohibitions against being outside the pomerium, the sacred boundary of Rome, overnight, sleeping out of his own bed for three consecutive nights, mounting a horse, looking at a legion under arms, swearing an oath, wearing most jewelry, eating leavened bread, touching a dead body, ivy, beans, a dog, raw meat or a she-goat, or having his hair or nails cut by a slave. The severe restrictions made it virtually impossible for a Flamen Dialis to attain high political office or enjoy the governorship of a province.

The Flamen Martialis was one of three flamines maiores, the flamines serving the three gods of the Archaic Triad (Jupiter, Mars and Quirinus), an important priest and member of the college of pontiffs. He was the special priest of the god Mars. Like the flamen dialis, he was subject to a number of taboos (though not, apparently, as restrictive as those surrounding the flamen dialis). One of his primary tasks was to lead public rites surrounding preparations for war, including shaking a sacred spear dedicated to Mars while the legions were departing.

The Flamen Dialis was one of three flamines maiores, the flamines serving the three gods of the Archaic Triad (Jupiter, Mars, and Quirinus). Quirinus was an ancient Roman state god. In all likelihood, he was originally a Sabine war god absorbed by the Romans. By the late Republic Quirinus was regarded as identical with the deified Romulus and was the god of Roman citizenship. Quirinus' chief priest was the Flamen Quirinalis, who was bound by many of the same strictures as other major flamines.

During the early Empire, it became common practice for Emperors to be deified upon their deaths - Vespasian famously mocked this custom when he murmured on his deathbed "Væ, puto deus fio." ("Alas,  I think I am becoming a god"). This imperial cult necessitated the appointment of additional flamines. The first such office was created in 40 BCE for Marc Antony, who became the first priest of the Divine Julius (Caesar the Dictator's deified persona). Many emperors had temples built in their honor during their lifetimes in the provinces (but only very rarely in Italy); these provincial cults were also presided over by priests bearing the title flamen. Caesar the Dictator, Augustus, Claudius, Trajan, Hadrian, Antoninus Pius, Marcus Aurelius, Commodus, Pertinax and Septimus Severus are a few of the emperors who, at some point in time, had independent cults dedicated to them.

PONTIFEX MAXIMUS The Office of Pontifex Maximus, the chief priest and executive of the priestly orders of the City of Rome, has endured longer, I believe, than any other functionary, sacred or profane. In a nearly unbroken line of succession stretching back to approximately 700 BCE, roughly 340 or so individuals have governed the religious life of the city under the same title, and in all that time the physical seat of the office has changed only three times; from the Palatine, to the Lateran, to the Vatican (the Papal residence was situated at a fourth locale: Avignon, France, 1309-1377). The time span involved covers some 53 percent of recorded human history.

The Rex Sacrorum ("King of Sacred Things") was a Roman pontiff. The position was created during the early Republic to take the place of the former kings, inasmuch as their office had included priestly functions as well as secular rulership, and these functions needed to be fulfilled regardless of a shift from monarchy to republic Thus, although the office wielded considerably less influence than the Pontifex Maximus (who appointed successive Reges to life terms), it nevertheless was by far the more prestigious position and was nominally the highest-ranking priest in Roman religion. His wife, the Regina Sacrorum, also held an important position in Roman religion. The Rex Sacrorum was forbidden to hold political office, out of concern that a politically active Rex might be in a position to revive the ancient monarchy. The Rex Sacrorum was the special priest of Janus, one of the chief gods of the Roman state, but also sacrificed to Jupiter. Other Latin towns, including Tusculum, Lavinium, and Velitrae, had similar positions, probably dating to the overthrow of their own kings, and in Athens, one of the archons (archon basileus) was designated as a sacral king each year.

VIRGO VESTALIS MAXIMA (Chief of the Order of Vestal Virgins) The Vestal Virgins (six in number throughout most of Roman history, although there were seven by the 4th century CE) were an Order of priestesses attendent to Vesta, Goddess of hearth and home. Unique within the Roman state religion, they were the only organized female sacerdotal order, and their chief (Virgo Vestalis Maxima) was the only female member of the College of Pontifices (the council of all the senior priests). Furthermore, in a culture in which women were chattals (without even so much as personal names), under perpetual authority of husband or most senior male relative, Vestal Virgins could own property, make wills, and vote in public elections. Regarded as being incapable of lying, they could give evidence without the usual oaths. Their person was sacrosanct - to injure or kill a Vestal Virgin was to commit treason. Their mere presence blessed the area around them - inasmuch as Vesta was the patroness of Innocence, a prisoner or slave could be freed if a priestess so much as touched them, and a condemned person being dragged to their execution was automatically pardoned if they chanced to encounter a Priestess along the way. Their responsibilities were awesome; they were the intercessors to the Goddess of the Homeland and, beyond the full panoply of ceremonies and festivals (culminating each year with the Vestalia on June 9), their chief office was the maintenance of the sacred and perpetual Fire of Vesta - should the Flame be extinguished for any reason, it was a sign that Vesta had turned Her face from Rome, and that the State would begin to wither and eventual die. They were a celibate order, to have sexual relations with a Vestal Virgin was to commit a double crime of both treason and (as they were Daughters of the State) incest. A virgin found to be unchaste was buried alive in the Campus Scleratus - but note; given that killing a Priestess, even a polluted one, was itself an act of treason, they were not simply thrown in a hole, but immurred in a doorless chamber with a few days-worth of food and water. They served their office for obligatory terms of thirty years, after which they could continue for life, or leave the Order and marry - few did so, since that would entail losing their unique privileges and surrendering to the authority of their husband like any ordinary Roman matron.