16.2. And the multitude of believers, both men and women, that were collected there [Alexandria] at the very outset, and lived lives of the most philosophical and excessive asceticism, was so great, that Philo thought it worth while to describe their pursuits, their meetings, their entertainments, and their whole manner of life.
17.1. It is also said that Philo in the reign of Claudius became acquainted at Rome with Peter, who was then preaching there.396 Nor is this indeed improbable, for the work of which we have spoken, and which was composed by him some years later, clearly contains those rules of the Church which are even to this day observed among us.
2. And since he describes as accurately as possible the life of our ascetics, it is clear that he not only knew, but that he also approved, while he venerated and extolled, the apostolic men of his time, who were as it seems of the Hebrew race, and hence observed, after the manner of the Jews, the most of the customs of the ancients.
. . .
22. These things the above-mentioned author has related in his own work, indicating a mode of life which has been preserved to the present time by us alone, recording especially the vigils kept in connection with the great festival, and the exercises performed during those vigils, and the hymns customarily recited by us, and describing how, while one sings regularly in time, the others listen in silence, and join in chanting only the close of the hymns; and how, on the days referred to they sleep on the ground on beds of straw, and to use his own words,\418/ "taste no wine at all, nor any flesh, but water is their only drink, and the relish with their bread is salt and hyssop."
23. In addition to this Philo describes the order of dignities which exists among those who carry on the services of the church, mentioning the diaconate, and the office of bishop, which takes the precedence over all the others.\419/ But whosoever desires a more accurate knowledge of these matters may get it from the history already cited.
24. But that Philo, when he wrote these things, had in view the first heralds of the Gospel and the customs handed down from the beginning by the apostles, is clear to every one.

 This tradition that Philo met Peter in Rome and formed an acquaintance with him is repeated by Jerome (de vir ill. 11), and by Photius (Cod. 105), who even goes further, and says directly that Philo became a Christian. The tradition, however, must be regarded as quite worthless. It is absolutely certain from Philo's own works, and from the otherwise numerous traditions of antiquity that he never was a Christian, and aside from the report of Eusebius (for Jerome and Photius do not represent an independent tradition) there exists no hint of such a meeting between Peter and Philo....

Furthermore, the hypothesis that Gnosticism arose from a failed Jewish apocalypticism, which Ehrman presents, is by no means certain. The two literary genres certainly have a great deal in common, and as far as we know apocalypticism does predate Gnosticism, and gnostic works (particularly Sethian) use a great many apocalyptic motifs. However, is this a case of Gnosticism being created by frustrated apocalypticists to explain why the eschaton did not come as planned or a case of literary borrowings between two groups with similar concerns? The latter idea is at least as possible as the former. There is at present no convincing consensus on the origins of Gnosticism: the apocalyptic derivation is one possibility among many and should have been signaled as such.

[and his footnote 3: For a good summation of the similarities, and also for a critique of the well-known theory of R. M. Grant that Gnosticism developed out of frustrated apocalyptic hopes in the aftermath of the first Jewish Revolt, see Keller, "Das Problem des Bo"sen in Apokalyptik und Gnostik," in Gnosis and Gnosticism: Papers Read at the Seventh International Conference on Patristic Studies (Oxford, September 8thoe13th 1975) (ed. M. Krause; NHS 8; Leiden: Brill, 1977), 70-90.]