Concordia is the Roman Goddess of Harmony. Unlike many other Goddesses Who were deified qualities, Concordia was worshipped from early times in Rome. She especially symbolized peace and agreement between the two classes of Rome, the plebeians or commoners, and the patricians or nobles. In the early days of Rome the two classes had joined to drive out the tyrannical Kings and created a Republic; but it quickly became a Republic of the patricians who had all the wealth and power. The plebeians were barred from the Senate and other governmental and priestly offices, though they of course made up most of the army. In 494 BCE the plebeians had had enough, and, refusing to serve in the army anymore, deserted and camped out on a hill near the Anio River that they called the Mons Sacer, or the Sacred Mountain. The patricians, left defenseless, came to some kind of sense and reforms were instituted giving the plebeians more rights.
To commemorate the compromises worked out between patricians and plebeians, a temple to Concordia was built in the northwestern end of the Roman Forum, backed up against the Capitoline Hill, near the Volcanal, a raised area that housed an altar to Vulcan. This temple was originally vowed in 367 BCE by the general Camillus and dedicated on July 22nd (which became Her festival) sometime afterwards. There was a statue of Victoria on its roof that was struck by lightning at one time; and the temple was restored in the 2nd century BCE. It was again restored by the Emperor Tiberius, who reopened it on the 16th of January, 10 CE, dedicating it to Concordia Augusta, the "Harmony of the Imperial Family". This temple was of somewhat unusual proportions due to the constraints of the site, but it was accorded one of the most beautiful in Rome, as it was finely made and entirely faced in marble. In later times it served as a museum of sorts, and many famous works of art were housed there.
Besides Her great temple in the Forum, Concordia had another, smaller temple on the Arx, the old citadel on the height of the Capitoline Hill, which was within sight of the larger temple to Concordia below it. Its dedication date was the 5th of February, and had been vowed by the praetor Manlius (a praetor being a kind of consul in charge of the armies) in 218 BCE after a rebellion among his troops was averted. She had another small temple, credited to the Empress Livia, probably in or near her colonnade, the porticus Liviae. It is called by the epithet magnifica ("splendid", "magnificent", or "sumptuous") by Ovid, and even though it can't have been very big, it must have been richly decorated. A temple to Concordia Nova ("New Harmony") was approved by the Senate in 44 BCE, and was to have been built in honor of Julius Caesar, though his assassination kind of put the kibosh on that and it was probably never built.
Concordia had a small bronze shrine near Her great temple in the Forum, set up in 304 BCE, but it is likely that it was demolished when the temple was expanded in the 2nd century BCE. It had been built by Cnaeus Flavius, an aedile who had published the very secret list of which days in the year were (ritually) acceptable for law cases to be heard. As cases heard on the wrong days were automatically dismissed, the fact that this calendar was jealously guarded by the patricians meant that plebeians submitting claims had a pretty good chance of having their claims denied out of hand. After Flavius published this calendar, the patricians were not at all happy with him, and he vowed the altar to Concordia to try to help smooth things out. The senate stuck it to him, though, by not requisitioning any funds to build it, and he had to use fines collected from money-lenders.
Concordia had a place in the festival of the Caristia or Charistia (meaning "Pardoning") of February 22nd, a holiday celebrated by families in which it was traditional to reconcile differences and to mend quarrels or feuds within the family. Concordia was invoked for Her powers of bringing harmony and agreement, and other Deities invoked at the Caristia were Janus, the double-faced God of New Beginnings, Salus, the Goddess of Health, and Pax, Goddess of Peace. These four Divinities were honored with statues grouped together at the Altar of Peace (not the great big famous one built by Augustus, but a smaller one whose location is unknown). They were also said to be worshipped together on the 30th of March and the 30th of January, and Concordia was invoked by matrons on April 1st at the Veneralia, the festival of Venus Verticordia, along with Fortuna and Venus Herself.
In the later days of the Empire, Concordia was worshipped as the bringer of marital harmony within the imperial family, and as such was called Concordia Augusta.
She was depicted as a matronly woman, veiled and heavily draped, holding an olive branch, emblematic of peace, and a cornucopia, to symbolize the abundance that can be achieved when people work together in harmony. She sometimes wore a crown and held a sceptre, caduceus, or patera, a small offering bowl from which libations were poured. She is associated with the stork, which symbolized family devotion to the Romans, and the dove, universally a symbol of peace and gentleness; and sometimes a star, as emblem of hope, is shown near Her. Another attribute of Concordia is the image of two clasped hands, both of which are right hands (like in a handshake), symbolizing two people agreeing. She is often shown on coins commemorating joint rule of leaders or the marriages of the imperial family.
The so-called Temple of Concordia in Akragas, Sicily, is a Doric-style temple built by Greek settlers to the island in the 6th and 5th centuries BCE. Though it is beautifully preserved, and the whole area is now in fact a World Heritage Site, the identification with Concordia is most probably wrong.
Inscriptions on coins refer to different applications of Concordia; these were probably not epithets, but rather illustrations of types of harmony, but I list some of them here: Concordia Militaris, "the Harmony of Armies", Concordia Provinciarum, "the Harmony of the Provinces", Concordia Conjugalis, "Harmony of Marriage".
She was identified with the Goddess Homonoia, the Greek personification of harmony.