Opening words from the World English Bible (public domain); the passage list is in-house
How we know the date
ISBE dates the beginning of the Greek Old Testament by the accession of the king who encouraged it, and counts the translation among the preparations for the spread of Christianity. ISBE's Old Testament chronology (1915) gives 280 BC.
Written in-house from the sources below · every year is a quotation
The sources, word for word
“Ptolemy Philadelphus, becoming king 280 BC, encouraged the translation of the Hebrew Scriptures into Greek, the result being the Septuagint version, and all it meant by way of preparation for the spread of Christianity.”