Quintus Julius Hilarianus

Quintus Julius Hilarianus (fl. 397), commonly known as Hilarian, was a Roman African chronographer and computist. He is sometimes identified with the bishop Hilarianus who attended the Council of Carthage in 411. This is uncertain and he may have even been a Donatist. His writings point to his having been a monk.^[1]

Hilarianus is known for two works in Latin:

• De ratione Paschae et mensis (or Expositum de die Paschae et mensis), completed on 5 March 397.^[1] It is a treatise about the importance of celebrating Easter.^[2] It has been read as a sermon,^[2] but this is not certain.^[1] It is used in the Carthaginian Computus of 455, which also cites a letter of one Agriustias to Hilarianus on the subject of computus.^[1]
• Chronologia siue Libellus de mundi duratione (or De cursu temporum), a treatise on salvation history written later in 397.^[1][2] It argues that the Second Coming will occur in 498, when the Earth is 6,000 years old. There will follow the thousand-year reign of Christ and a final battle. Since the end of the world is placed beyond the lifetime of Hilarianus or his initial audience, the Libellus does not seem to be a response to contemporary events but "a statement about hope for life eternal". Its brand of millenarianism, however, soon came to be regarded as heresy, making Hilarianus "one of [its] last vocal proponents".^[2] Nevertheless, in two groups of manuscripts the Libellus was incorporated into the compilation known as the Chronicle of Fredegar. In one group, it replaces the contribution of the Liber generationis.^[3] The 9th-century manuscript Reginensis 213 opens with it.^[4][5]

Some scholars have suggested Hilarianus as the author of the Liber genealogus.^[6]