Felicitas had a temple in Rome as early as the mid-2nd century BC, and during the Republican era was honored at two official festivals of Roman state religion, on July 1 in conjunction with Juno and October 9 as Fausta Felicitas. Felicitas continued to play an important role in Imperial cult, and was frequently portrayed on coins as a symbol of the wealth and prosperity of the Roman Empire. Her primary attributes are the caduceus and cornucopia. The English word "felicity" derives from felicitas.
In its religious sense, felix means "blessed, under the protection or favour of the gods; happy." That which is felix has achieved the pax divom, a state of harmony or peace with the divine world. The word derives from Indo-European *dhe(i)l, meaning "happy, fruitful, productive, full of nourishment." Related Latin words include femina, "woman" (a person who provides nourishment or suckles); felo, "to suckle" in regard to an infant; filius, "son" (a person suckled); and probably fello, fellare, "to perform fellatio", with an originally non-sexual meaning of "to suck". The continued magical association of sexual potency, increase, and general good fortune in productivity is indicated by the inscription Hic habitat Felicitas ("Felicitas dwells here") on an apotropaic relief of a phallus at a bakery in Pompeii.
In archaic Roman culture, felicitas was a quality expressing the close bonds between religion and agriculture. Felicitas was at issue when the suovetaurilia sacrifice conducted by Cato the Elder as censor in 184 BC was challenged as having been unproductive, perhaps for vitium, ritual error. In the following three years Rome had been plagued by a number of ill omens and prodigies (prodigia), such as severe storms, pestilence, and "showers of blood," which had required a series of expiations (supplicationes). The speech Cato gave to justify himself is known as the Oratio de lustri sui felicitate, "Speech on the Felicitas of his Lustrum", and survives only as a possible quotation by a later source. Cato says that a lustrum should be found to have produced felicitas "if the crops had filled up the storehouses, if the vintage had been abundant, if the olive oil had flowed deliberately from the groves", regardless of whatever else might have occurred. The efficacy of a ritual might be thus expressed as its felicitas.
The ability to promote felicitas became proof of one's excellence and divine favor. Felicitas was simultaneously a divine gift, a quality that resided within an individual, and a contagious capacity for generating productive conditions outside oneself: it was a form of "charismatic authority". Cicero lists felicitas as one of the four virtues of the exemplary general, along with knowledge of military science (scientia rei militaris), virtus (both "valor" and "virtue"), and auctoritas, "authority." Virtus was a regular complement to felicitas, which was not thought to attach to those who were unworthy. Cicero attributed felicitas particularly to Pompeius Magnus ("Pompey the Great"), and distinguished this felicitas even from the divine good luck enjoyed by successful generals such as Fabius Maximus, Marcellus, Scipio the Younger and Marius.
The sayings (sententiae) of Publilius Syrus are often attached to divine qualities, including Felicitas: "The people's Felicitas is powerful when she is merciful" (potens misericors publica est Felicitas).