Josephus on John the baptizer.

What did Josephus write about John the baptist?

What Josephus wrote about John the baptist is often discussed in conjunction with the Testimonium Flavianum or the testimony to James, as it speaks of a character otherwise known in near contemporary literature only through the New Testament.

Josephus, Antiquities of the Jews 18.5.2 §116-119:

Τισι δε των Ιουδαιων εδοκει ολωλεναι τον Ηρωδου στρατον υπο του θεου και μαλα δικαιως τινυμενου κατα ποινην Ιωαννου του επικαλουμενου βαπτιστου. κτεινει γαρ δη τουτον Ηρωδης αγαθον ανδρα και τοις Ιουδαιοις κελευοντα αρετην επασκουσιν και τα προς αλληλους δικαιοσυνη και προς τον θεον ευσεβεια χρωμενοις βαπτισμω συνιεναι· ουτω γαρ δη και την βαπτισιν αποδεκτην αυτω φανεισθαι μη επι τινων αμαρταδων παραιτησει χρωμενων, αλλ εφ αγνεια του σωματος, ατε δη και της ψυχης δικαιοσυνη προεκκεκαθαρμενης. και των αλλων συστρεφομενων, και γαρ ησθησαν επι πλειστον τη ακροασει των λογων, δεισας Ηρωδης το επι τοσονδε πιθανον αυτου τοις ανθρωποις μη επι αποστασει τινι φεροι, παντα γαρ εωκεσαν συμβουλη τη εκεινου πραξοντες, πολυ κρειττον ηγειται πριν τι νεωτερον εξ αυτου γενεσθαι προλαβων ανελειν του μεταβολης γενομενης [μη] εις πραγματα εμπεσων μετανοειν. και ο μεν υποψια τη Ηρωδου δεσμιος εις τον Μαχαιρουντα πεμφθεις το προειρημενον φρουριον ταυτη κτιννυται. τοις δε Ιουδαιοις δοξαν επι τιμωρια τη εκεινου τον ολεθρον επι τω στρατευματι γενεσθαι του θεου κακωσαι Ηρωδην θελοντος.

Now some of the Jews thought that the destruction of the army of Herod came from God, and that very justly as a punishment of what he did against John, the one called the baptist; for Herod slew him, who was a good man and commanded the Jews to exercise virtue, as to both justice toward one another and piety toward God, and so to come to baptism; for thus the baptism would be acceptable to him, if they made use of it, not in order to forgive some sins, but rather for the holiness of the body, supposing still that the soul was thoroughly cleansed beforehand by justice. Now when others came in crowds about him, for they were very greatly pleased by hearing his words, Herod, who feared lest the great influence John had over the people might put it into his power and inclination to raise a rebellion, for they seemed ready to do any thing he should advise, thought it best to prevent any mischief he might cause by putting him to death, not to bring himself into difficulties by sparing a man who might make him repent of it when it would be too late. Accordingly he was sent a prisoner, out of the suspicious temper of Herod, to Machaerus, the castle I before mentioned, and was there put to death. Now the Jews had an opinion that the destruction of this army was sent as a punishment upon Herod, and a mark of the displeasure of God to him.

I recommend going through the catalogue of citations compiled by David C. Hindley, which list includes a number of references to this passage.

From Origen, Against Celsus 1.47:

Εν γαρ τω οκτωκαιδεκατω της Ιουδαικης αρχαιολογιας ο Ιωσηπος μαρτυρει τω Ιωαννη ως βαπτιστη γεγενημενω και καθαρσιον τοις βαπτισαμενοις επαγγελλομενω.

For in the eighteenth [book] of the Judaic Antiquities Josephus witnesses to John as the one who became the baptist and promised cleansing for those baptized.

Regarding this passage John P. Meier remarks in volume 2 of A Marginal Jew, page 66, note 6:

It may be that Origen does not cite Josephus verbatim because Josephus' insistence that John's baptism confers only bodily purification and not forgiveness of sins contradicts the statement of Mark 1:4....

This, I think, is a reasonable conjecture. Mark 1.4 and Luke 1.3, of course, claim that John was baptizing precisely for the forgiveness of sins (εις αφεσιν αμαρτιων).