Donatus Magnus, also known as Donatus of Casae Nigrae, became leader of a schismatic Christian sect known as the Donatists in North Africa. He is believed to have died in exile around 355.
Little is known of his earlier life because of the complete loss of his correspondence and written works. He first appears in Church records as Donatus of Casae Nigrae in October 313 when Pope Miltiades found him guilty of re-baptizing clergy who had lapsed and of forming a schism within the Church.
Casae was a settlement located on the extreme southern edge of the plains of Numidia, south of Theveste, an area settled by people predominantly of Berber descent.
These events may have taken place before Donatus arrived in Carthage, probably before 311.
Donatus was consecrated in 313 AD as Bishop of Carthage and Primate of North Africa, the leader of the Christian sect which came to be known as the Donatist sect, even though Donatus was not the founding leader, but rather followed the founding leader Majorinus.
The background to the controversy was the wave of persecutions of Christians by the Roman Emperor Diocletian. At that time some Church leaders - unwilling to endure torture or death and become martyrs - had been ready to take such acts as worshipping the gods of the old pantheon, considered idols by Christians, or surrendering church books and property to the imperial authorities. Such people became known as “traditors” ("surrenderers"). One of these "traditors", named Caecilian, had returned to the fold of the Church once the persecutions ended, and was consecrated Bishop of Carthage and Primate of North Africa. Those of the faithful who refused to accept the authority of such a spiritual leader raised Majorinus as a rival bishop; however, Majorinus died shortly after being consecrated, and it fell to Donatus to take his place and continue the struggle.