The so-called Letter of Aristeas or Letter to Philocrates  is a Hellenistic work of the second century BCE, one of the Pseudepigrapha. Josephus Flavius who rephrases some of the letter, ascribes it to Aristeas and written to Philocrates, describing the Greek translation of the Hebrew Law by seventy-two interpreters sent into Egypt from Jerusalem at the request of the librarian of Alexandria, resulting in the Septuagint translation. Though its story of the creation of the Greek translation of the Hebrew Bible is fictitious, but it is the earliest text to mention the Library of Alexandria.
The Content of the Letter
The Letter of Aristeas is dedicated to Philocrates, brother of the author of the letter, in this way: “My brother in character no less than in blood, but one with me as well as in the pursuit of goodness.” It begins by telling how King Ptolemy Philadelphus  (285-247 BCE) was advised by his librarian to have the laws of the Jews translated for his library of 200,000 volumes which had no translation of the sacred scriptures of the Jews (1-8). Ptolemy selects Aristeas to go on an embassy to the high priest Eliezer with the request to send a body of scholars to translate their sacred scriptures into Greek. Aristeas takes the opportunity to suggest to Ptolemy the freeing of the 30,000 men whom his father had brought from Palestine as garrisons for the country districts (17-27). The king agrees to free the Jews and also pays their owners 20 drachmae per head, the total being 660 talents (28-40).
Eleazar answers Ptolemy’s request favorably (41-50). The king then sends a gift of 100 talents of silver to Eliezer for the temple sacrifices: a sacred table ( 51-72), gold and silver bowls (73-78), and golden vials (79-82).
A most interesting account of the temple, city, and country is then given (107-120), which is believed to be from a lost work of Hecate. The translators selected by the high priest leave for Egypt (121-127). This is followed by a disquisition on the enactment of laws that treat of food, which are justified by means of the allegorical method (128-171). Ptolemy accords the Jewish elders great deference (vv. 172-186), entertains them at a banquet for seven successive days, and is delighted with the answers to the 72 questions given by the leaders from Judea (187-300).
At the end of the week the elders are installed on the island of Pharos, where they work every day and complete their translation in 72 days (201-311). The translation is read before the Jewish population and recognized by the latter to be accurate (312-317). Any person who tampers with it in the future is to be subject to a curse. The king receives the scrolls with great satisfaction and dismisses the translators, who return to Jerusalem with costly gifts (318-322).
Manuscripts and Criticism
Over twenty manuscripts of this letter are preserved and it is often mentioned and quoted in other texts. Its supposed author, purporting to be a courtier of Ptolemy II Philadelphus (reigned 281-246 BCE) is most often referred to as pseudo-Aristeas.
There has been a long debate among scholars regarding whether the Letter tells us anything historically reliable about the translation of the law into Greek. It is not impossible that the process happened or started in Philadelphus’s reign since use of the translation is attested by ca. 200 BCE. It seems unlikely on general grounds that it all transpired just as the Letter claims. It is possible that the Letter was written in part to defend the validity of the Torah in Greek in face of claims made for the sole sufficiency of the Hebrew version. In later Christian retellings of the story about the translation found in the Letter, the tale expanded so that eventually the entire Hebrew Bible was involved (so Justin Martyr, Dialogue with Trypho 68:6-7); indeed, all the translators worked on the entire project independently, and when they compared their results at the end, wonder of wonders, every one of them was exactly alike (Irenaeus, Against Heresies 3.21.2).” 
A main goal of the second-century author seems to be to establish the superiority of the Greek Septuagint text over any other version of the Hebrew Bible. The author is noticeably pro-Greek, portraying Zeus as simply another name for Hashem, and while criticism is lodged against idolatry and Greek sexual ethics, the argument is phrased in such a way as to attempt to persuade the reader to change, rather than as a hostile attack. The manner in which the author concentrates on describing Judaism, and particularly its temple in Jerusalem could be viewed as an attempt to proselytize.
 Harris, Stephen L., Understanding the Bible. (Palo Alto: Mayfield) 1985
 The tradition preserved in the pseudepigraphical Letter of Aristeas which connects the Septuagint translation of the Old Testament into Greek with his patronage is probably overdrawn. However, most of the scholars belives, “There can be little doubt that the Law was translated in Philadelphus’s time since Greek quotations from Genesis and Exodus appear in Greek literature before 200 BCE. The language of the Septuagint is more like Egyptian Greek than it is like Jerusalemite Greek (Bregman, Ahron. A History of Israel, p. 467)
 VanderKam James C. An Introduction to Early Judaism, Grand Rapids, MI Eerdmans pp. 84-85