The Diocletianic Persecution, the last and most severe episode of the persecution of Christians in the Roman Empire, began with the publication of a first edict by Roman emperor Diocletian.

The Diocletianic or Great Persecution was the last and most severe persecution of Christians in the Roman Empire. In 303, the emperors Diocletian, Maximian, Galerius, and Constantius issued a series of edicts rescinding Christians' legal rights and demanding that they comply with traditional religious practices. Later edicts targeted the clergy and demanded universal sacrifice, ordering all inhabitants to sacrifice to the Roman gods. The persecution varied in intensity across the empire—weakest in Gaul and Britain, where only the first edict was applied, and strongest in the Eastern provinces. Persecutory laws were nullified by different emperors at different times, but Constantine and Licinius' Edict of Milan in 313 has traditionally marked the end of the persecution.

The persecution of Christians can be traced from the first century of the Christian era to the present day. Christian missionaries and converts to Christianity have both been targeted for persecution, sometimes to the point of being martyred for their faith, ever since the emergence of Christianity.

The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Romans conquered most of this during the Republic, and it was ruled by emperors following Octavian's assumption of effective sole rule in 27 BC. The western empire collapsed in 476 AD, but the eastern empire lasted until the fall of Constantinople in 1453.

An edict is a decree or announcement of a law, often associated with monarchies, but it can be under any official authority. Synonyms include "dictum" and "pronouncement". Edict derives from the Latin edictum.