1 Peter 5:13

She that is in Babylon, elect together with you

(η εν Βαβυλων συνεκλεκτη). Either actual Babylon or, as most likely, mystical Babylon (Rome) as in the Apocalypse. If Peter is in Rome about A.D. 65, there is every reason why he should not make that fact plain to the world at large and least of all to Nero. It is also uncertain whether η συνεκλεκτη (found here alone), "the co-elect woman," means Peter's wife (1 Corinthians 9:5) or the church in "Babylon." The natural way to take it is for Peter's wife. Cf. εκλεκτη κυρια in 2 John 1:1 (also verse 2 John 1:13).Mark my son

(Μαρκος ο υιος μου). So this fact agrees with the numerous statements by the early Christian writers that Mark, after leaving Barnabas, became Peter's "interpreter" and under his influence wrote his Gospel. We know that Mark was with Paul in Rome some years before this time (Colossians 4:10).