The Era of the Martyrs (Latin: anno martyrum), also known as the Diocletian era (Latin: anno Diocletiani), is a method of numbering years based on the reign of Roman Emperor Diocletian who instigated the last major persecution against Christians in the Empire.
Annianus of Alexandria, a monk who flourished at the beginning of the 5th century, placed the epoch of his world era on 25 March 5492 BC by counting back eleven 532-year paschal cycles from anno Diocletiani 77, itself four 19-year lunar cycles after anno Diocletiani 1.
Regarded as a civil rather than a religious era, it began on the first day of the Alexandrian year, 29 August 5493 BC.
When Dionysius Exiguus, an Eastern Roman of Scythia Minor, inherited the continuation of those tables for an additional 95 years (in the year 525 AD) he replaced the anno Diocletiani era with one based on the birth of Christ: the anno Domini era.
[1] The anno Domini era became dominant in the Latin West but was not used in the Greek East until modern times.