Varronian chronology

The Varronian chronology is the commonly accepted chronology of early Roman history named after the Roman antiquarian Marcus Terentius Varro. It is from this chronology that the commonly used dates for the foundation of the city, the overthrow of the monarchy, the Decimvirates, the Gallic sack of Rome, and the first plebeian consul are derived. The chronology consists of an ordered list of magisterial colleges which, in modern times, are regularly assigned to years BC.
The years given by the Varronian chronology prior to 300 BC should not be accepted as absolute dates. Years in the chronology are also demonstrably incorrect and it flows four years prior to actual events by 340 BC. Moreover, Roman historians and antiquarians also did not all use Varro's scheme. Because both the ordering and absolute position of Varronian years is not well established for this early period, the numeric years derived from it should be taken as "no more than numerical symbols for specific consular years".
Because the Varronian chronology places the foundation of Rome on 21 April 753 BC, it is also the basis for the Varronian years ab urbe condita. Other chronologies place Rome's foundation in different years BC, meaning that they would place the same event in different years AUC. Romans of the historical period did not use the Varronian chronology or ab urbe condita for everyday timekeeping. Dates were instead kept in reference to a certain year's consuls: eg that an event occurred during the consulship of Marcus Tullius Cicero and Gaius Antonius Hybrida.

Construction

The ancient Romans customarily reckoned years by consular dating. For example, the year AD 1 was not assigned a number in a sequence, as modern years are reckoned, but rather a name: in this instance the year of the consulship of Gaius Caesar and Lucius Aemilius Paullus. Determining when a recorded event occurred therefore requires knowing the names of the consuls as a reference, for which there are accurate records back to 300 BC. Prior to that point, however, records are fragmentary and many Romans reconstructed those records into differing consular sequences. Livy and Dionysius of Halicarnassus in their respective works – Ab urbe condita and Roman Antiquities – used separate schemes which place the same consuls in different years.
The specific years BC assigned by the various chronologies to consular colleges should be taken as an unordered numeric identifier for those colleges rather than absolute years. The chronologies differ largely in how they order the consular colleges and how many such colleges they have between any two specific consular years.

Problems

Roman records prior to around 300 BC were fragmentary or incomplete. The ancient Roman historians, writing centuries after the events they purport to describe, were themselves unclear about the order or identities of some magisterial years. The most well known problems are with the fictitious "dictator" and "anarchy years".
The Varronian years 333, 324, 309, and 301 BC, the "dictator years", are supposed to have had a dictator and magister equitum hold office in place of the normal consuls. They are, however, largely rejected by modern scholars as a fabrication. They appear nowhere in other late republican sources. Moreover, removal of these four fictitious years is further supported by modern astronomy. Livy records an eclipse during the consulship of Gaius Marcius Rutilus and Titus Manlius Torquatus which corresponds to the Varronian year 344 BC. Modern astronomy, however, dates the same event to 15 September 340 BC, indicating that Varro placed those consuls four years prior to their absolute dates.
A separate five year period, called the "anarchy years", occurred in the Varronian years 375–371 BC. No magistrates were allegedly elected. No trace of these "anarchy years" is present in the earlier works of Fabius Pictor. These were likely added to synchronise Roman and Greek histories by lengthening the Roman fourth century BC. The years are likely not historical – and are regardless not recorded by Diodorus, who reports only one year of anarchy, but are recorded in ancient historiography as far back as Polybius. The "anarchy years" are also widely rejected by scholars.

Adoption and legacy

The Varronian chronology was adopted by the Roman state during the first century BC and gave rise to the traditional years ab urbe condita ; most especially, those dates were used in monumental Augustan-era inscriptions, the fasti Capitolini and the fasti Triumphales.
T R S Broughton, in the Magistrates of the Roman republic, on examination of the "dictator years" instead put forward the Livian chronology as an alternative. Tim Cornell, in Beginnings of Rome, instead prefers the Dionysian chronology. However, use of the "official" chronology passed from the Roman state is well-entrenched in modern historiography.