Albert Barnes Commentary Ezra 4:15

"that search may be made in the book of the records of thy fathers: so shalt thou find in the book of the records, and know that this city is a rebellious city, and hurtful unto kings and provinces, and that they have moved sedition within the same of old time; for which cause was this city laid waste." — Ezra 4:15 (ASV)

The book of the records - Compare Esther 2:23; Esther 6:1; Esther 10:2. The existence of such a “book” at the Persian court is attested also by Ctesias.

Of your fathers - That is, your predecessors on the throne, Cambyses, Cyrus, etc. If Artaxerxes was the Pseudo-Smerdis (Ezra 4:7; see note), these persons were not really his “fathers” or ancestors; but the writers of the letter could not venture to call the king an impostor.