Annus Domini (Year of the Incarnation)
Lat. Annus Domini ('Year of our Lord')
The Christian calendar reckoning numbering years from the presumed incarnation and birth of Jesus Christ, invented by Dionysius Exiguus in the sixth century.
Anglo-Saxon England was the first society in Europe to use the *Annus Domini* system routinely in public legal documents, pioneered in eighth-century diplomas and canonised by the Venerable Bede.
Indictio (The Indiction)
Lat. indictio ('proclamation of assessment') < indicere ('to declare')
A 15-year recurring fiscal calendar cycle originally instituted by Emperor Constantine the Great in A.D. 312, universally adopted by early Christian chanceries to date documents alongside the calendar year.
Because indiction numbers cycle from 1 to 15, comparing the recorded indiction against the recorded Year of the Incarnation provides modern diplomatic scholars with an infallible check on the authenticity of a diploma.
Regnal Year (Annus Regni)
Lat. annus regni ('year of the reign')
The chronological method of dating documents by the completed years of a reigning monarch's rule, beginning on the day of their accession or formal consecration.
Often combined in diplomas with the Year of Grace and the indiction, establishing precise synchronisation between civil chronology and sacred history.