Fasti (Lat. Dies fasti), those days among the ancient Romans on which it was lawful to transact legal or public business, in opposition to nefasti, on which it was not permitted. But the sacred books, in which the lawful days of the year were marked, were themselves denominated fasti, and the term was employed, in an extended sense, to signify various kinds of registers, especially the Fasti Sacri or Kalendares, and the Fasti Annales or Historici.
The Fasti Kalendares or calendars of the year were kept exclusively by the priests for about four centuries and a half after the building of the city. The appearance of the new moon was proclaimed by a pontifex, who at the same time announced to the people the time which would intervene between the Kalends and the Nones. On the Nones the country-people assembled for the purpose of learning from the Rex Sacrorum the various festivals of the month, and the days on which they would fall. In the same way those who intended to go to law learned on what days it would be right (fas) to do so. The mystery with which this lore was surrounded, for purposes of power and profit, by the favoured class was dispelled by Cn. Flavius, the scribe of App. Clandius Cæcus, who surreptitiously copied from the pontifical book the requisite information, and published it to the people in the forum. Consequently time-tables (fasti) became common, very much resembling modern almanacs. They contained the days and months of the year, the Nones, Ides, lawful and unlawful days, &c., astronomical observations on the rising and setting of the fixed stars, the commencement of the seasons, brief notices concerning the introduction and signification of certain rites, the dedication of temples, the dates of victories, disasters, and the like. In later times the exploits and honours of the imperial family were duly entered in the calendar. The celebrated Fasti of Ovid is a sort of poetical year-book or companion to the almanac, as arranged by Julius Cæsar, who remodelled the Roman year.
Several very curious specimens of fasti on stone and marble have been discovered, of which the most remarkable are the Kalendarium Maffeanum (so called from its first possessor), upon almost all the days of the year; the Kalendarium Prænestinum of Verrius Flaccus, discovered in 1770 at Præneste, containing the months January to April and December; the Kalendarium Vatieinum (March, April, August), Venusinum (May, June), Esquilinum (May and June), and Farnesianum (February and March). These are printed in vol. i. of Mommsen's Corpus Inscriptionum Latinarum (Berlin, 1863), in which the Roman calendar for almost the complete year is elucidated.
The Fasti Annales or Historiei were chronicles containing the names of the consuls and other magistrates of the year, and an enumeration of the most remarkable events in the history of Rome, noted down opposite the days on which they occurred. From its application to these chronicles the word fasti came to be used by the poets as synonymous with historical records. Of these, fragments have come down to us, of which the most important are the so-called Fasti Capitolini, discovered in the neighbourhood of the ancient forum in the 16th and 19th centuries. See CALENDAR; also Boor, Die Fasti Censorii (1873), and Wehrmann, Die Fasti Prætorii (1875).