He wrote a Treatise of Heresies, wherein he reckons 20 Heresies before the Birth of Jesus Christ, and 128 afterwards to the Year 380, in which he wrote, and tells in a few Words the principal Errors of each of them. St. Austin observes at the beginning of his Book about Heresies, that it was a sur∣prizing thing that Philastrius who was much less learned and less exact than St. Epiphanius, should reckon up many more Heresies than he did; from whence he concludes, that these two Authors could not have the same Notions of Heresy, because indeed it is very difficult to give a just Definition of it. Wherefore, adds St. Austin, in giving the Catalogue of Heresies, we must carefully avoid these two opposite extremes, whereof one is to make those Heresies that are not, and the other is to omit those Heresies which really are such. 'Tis a rare thing for those who make the Catalogues of Heresies to fall into this last Fault; but the first is very common, and Philastrius was more subject to it than any body. For he feigns a multitude of Heresies that never were , and sometimes he puts in the num∣ber of Heresies those Opinions that are true, or at least problematically disputed . And therefore we need not wonder, that he made so numerous a Catalogue of Heresies, which he also multiplied, by mentioning one and the same Heresy many times.
The Stile of this Author is mean and flat; he had no great Learning, and has committed many gross Faults in this little Tract, which is not written with any exactness: Yet there are some re∣markable things in it .
This Treatise was printed at Basle in 1528; and at Helmstadt in 1611, and in 1614, and with St. Austin's Book of Heresies, in several places, and in the Bibliotheca Patrum.