Pope John III (Latin: Ioannes III) was Pope from 17 July 561 to his death in 574. He was born in Rome of a distinguished family. The Liber Pontificalis calls him a son of one Anastasius. His father bore the title illustris, more than likely being a vir illustris ("illustrius man", high-ranking member of the Roman Senate). According to the historian Evagrius, his birth name was Catelinus, but he took the name John on his accession.
He may be identical with the subdeacon John who made a collection of extracts from the Greek Fathers and completed the translation of the Vitae patrum into Latin which Pope Pelagius I had begun.
His pontificate is characterized by two major events over which he had no control. The first was the death of Emperor Justinian I in 565. Jeffrey Richards considers his reign was an "anomaly", "a temporary damming up of the stream of history." With his death, the Byzantine Empire turned its attention from Rome and the West to pressing problems in the Balkans, from the Avars, Persians and the Arabs. "Italy, being geographically peripheral to the imperial heartland, inevitably took bottom place on the strategic priority list."
The other major event was the invasion of the Lombards, which began in 568. Much of northern Italy was overrun, as well as the central spine of the peninsula, making a shambles of the imperial administration. Further, their warriors threatened the survival of Rome herself, subjecting the Eternal City to repeated sieges. Lastly, their entrance reintroduced the newly extinguished Arian belief, which threatened the predominance of Roman Catholicism.