Pĕlăgĭus | Pĕlăgĭānus, i (noun M.m) : * A famous heretic of the fifth century A. D., Aug. Ep. 175; id. Haeres. 88.—Hence, , , , a follower of Pelagius, Isid. Orig. 8, 5, 63.
Charlton T. Lewis, Charles Short, A Latin Dictionary
PIR
Male Personal name Confirmed occurences in the Roman Empire:
Aurelius Antoninus Pelagius (Masc, eques), ref: PIR A 1448 | PIR ID2447