This epistle is the only writing of Polycrates which is preserved to us. This passage, with considerably more of the same epistle, is quoted below in Bk. V. chap. 24. From that chapter we see that the epistle was written in connection with the Quarto-deciman controversy, and after saying, “We therefore observe the genuine day,” Polycrates goes on in the words quoted here to mention the “great lights of Asia” as confirming his own practice. (See the notes upon the epistle in Bk. V. chap. 24.) The citation here of this incidental passage from a letter upon a wholly different subject illustrates Eusebius’ great diligence in searching out all historical notices which could in any way contribute to his history.