In the Roman religion

Religion in ancient Rome

Religion in ancient Rome encompassed the religious beliefs and cult practices regarded by the Romans as indigenous and central to their identity as a people, as well as the various and many cults imported from other peoples brought under Roman rule. Romans thus offered cult to innumerable deities...

, Regifugium or Fugalia was an annual observance that took place every February 24. In Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

, the name of the observance transparently means "flight of the king

Monarch

A monarch is the person who heads a monarchy. This is a form of government in which a state or polity is ruled or controlled by an individual who typically inherits the throne by birth and occasionally rules for life or until abdication...

."

What exactly this observance was occasioned by is a matter of some controversy. According to Varro

Varro

Varro was a Roman cognomen carried by:*Marcus Terentius Varro, sometimes known as Varro Reatinus, the scholar*Publius Terentius Varro or Varro Atacinus, the poet*Gaius Terentius Varro, the consul defeated at the battle of Cannae...

 and Ovid

Ovid

Publius Ovidius Naso , known as Ovid in the English-speaking world, was a Roman poet who is best known as the author of the three major collections of erotic poetry: Heroides, Amores, and Ars Amatoria...

, this was a festival commemorating the flight of the last king of Rome

Roman Kingdom

The Roman Kingdom was the period of the ancient Roman civilization characterized by a monarchical form of government of the city of Rome and its territories....

, Tarquinius Superbus, in 510 BC. Ovid's Fasti

Fasti

In ancient Rome, the fasti were chronological or calendar-based lists, or other diachronic records or plans of official and religiously sanctioned events...

contains the longest surviving account of the observance; he begins:

Nunc mihi dicenda est regis fuga. Traxit ab illa
     sextus ab extremo nomina mense dies.
Ultima Tarquinius Romanæ gentis habebat
     regna, vir iniustus, fortis ad arma tamen.

(Now I must tell of the flight of the King, six days¹ from the end of the month. The last of the Tarquins possessed the Roman nation, an unjust man, but nevertheless strong in war.)

Plutarch

Plutarch

Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

 disagrees; he holds that since the Rex Sacrorum

Rex Sacrorum

In ancient Roman religion, the rex sacrorum was a senatorial priesthood reserved for patricians. Although in the historical era the pontifex maximus was the head of Roman state religion, Festus says that in the ranking of priests, the rex sacrorum was of highest prestige, followed by the flamines...

, substitute for the former king of Rome in various religious rituals, held no civic or military role, but nevertheless was bound to offer a public sacrifice

Sacrifice

Sacrifice is the offering of food, objects or the lives of animals or people to God or the gods as an act of propitiation or worship.While sacrifice often implies ritual killing, the term offering can be used for bloodless sacrifices of cereal food or artifacts...

 in the Comitia on this date, the "flight of the king" was the swift exit the proxy king was required to make from that place of public business.

The two theories can be reconciled if we take the custom of swift exit required of the Rex Sacrorum

Rex Sacrorum

In ancient Roman religion, the rex sacrorum was a senatorial priesthood reserved for patricians. Although in the historical era the pontifex maximus was the head of Roman state religion, Festus says that in the ranking of priests, the rex sacrorum was of highest prestige, followed by the flamines...

to be nothing more than a remembrance of the flight of Tarquinius Superbus.

Note

¹Inclusively, as the Romans were wont to count. See nundinae at Roman calendar