first accounts

First pagan accounts of Catholicism:
 
A.D. 112
Epistulae X 96
Pliny the Younger, 61-113, Roman Governor of Bithynia and Pontus, sends a letter to Emperor Trajan (r. 98-117) asking for counsel on what to do with Catholics who have been put on trial following anonymous accusations.
 
A.D. 115/16
Annals
Tacitus, 56-120, Roman politician/historian, references the crucifixion of Christ in connection with Emperor Nero (r. 54-68) and his persecution of Catholics.
 
A.D. 121/22
Lives of the Twelve Caesars
Suetonius, 69-122, Roman historian, writes about an expulsion from Rome of Jews by Emperor Claudius (r. 41-54) and punishments exacted by Emperor Nero and that the actions taken were caused by disturbances instigated by a certain ‘Chrestus’ [sic].

Manuscript Tradition
The manuscripts that preserve a given work are collectively called its tradition. As every act of copying introduces fresh errors, the extant writings differ among themselves and from the lost original. As you read, recall that medieval monks were the copy machines of the time. Verified by scholars:

• Pliny – His letters survived through copies made hundreds of years later. See https://www.hs-augsburg.de/~harsch/augustana.html
• Tacitus – Only half of 30 books survived. The first six books survived in a single manuscript written in Germany about A.D. 1000, probably at the Benedictine Abbey of Fulda and are now in Florence at the Biblioteca Medicea Laurenziana. Books 11-16 survived in a single manuscript written at the Benedictine Abbey of Monte Cassino and are preserved in the Laurentian Library.
• Suetonius – The oldest surviving copy of Twelve Caesars was made in Tours, France, in the late 8th or 9th century and is currently held in the Bibliothèque nationale de France.