A major event occurred during the reign of Ptolemy II Philadelphus. This was the translation of the Torah into Greek. This translation eventually evolved into the Greek translation of the Torah known as the Septuagint. There are several ancient sources that discuss this event, but, unfortunately (and unsurprisingly), these sources frequently disagree on important details. The main traditional Jewish sources that describe the incident are the Talmud (Megillah 9a), Mesechta Sofrim 1:8-9, and Megillas Taanis. The story is also discussed in other, non-traditionally authoritative, sources such as Josephus (Antiquities XII:2), Philo (Life of Moses V-VII), and the Letter of Aristeas. The Letter of Aristeas is, or purports to be, a letter written by a non-Jewish advisor of Ptolemy Philadelphus named Aristeas recounting the story of the translation of the Torah. The Letter of Aristeas is the primary source for the story as told by Josephus, and appears to have been a source for Philo, but there are some differences between all these sources.
The Talmud (Megillah 9a) gives the following account:
דתניא, מעשה בתלמי המלך שכינס שבעים ושנים זקנים והכניסן בשבעים ושנים בתים ולא גילה להם על מה כינסן ונכנס אצל כל אחד ואחד ואמר להם, "כתבו לי תורת משה רבכם." נתן הקב"ה בלב כל אחד ואחד עצה והסכימו כולן לדעת אחת וכתבו לו, "אלקים ברא בראשית" וכו' ע"ש
It is taught, an incident occurred with Ptolemy the king that he gathered seventy-two elders and put them into seventy-two houses and he did not reveal to them why he had gathered them. He went in to each one of them and told him, "Write for me the Torah of Moses your teacher." The Holy One, blessed be He, gave counsel to the heart of every one of them and they all came to the same opinion and they wrote for him, "God created in the beginning" etc.
The basic story is that Ptolemy gathered together seventy-two sages and made each Sage write a translation of the Torah into Greek. A miracle occurred and the Sages, all working independently, wrote exactly the same translation, including several changes from the literal meaning of the Torah that were necessary to prevent the Torah from being misinterpreted or misused by the Greeks.
In Mesechta Sofrim (1:7-8) we are told that there were actually two distinct incidents where the Torah had been translated at the command of one of the Ptolemies:
מעשה בה' זקנים שכתבו לתלמי המלך את התורה יונית והיה היום קשה לישראל כיום שנעשה העגל שלא היתה התורה יכולה להתרגם כל צרכה.
שוב מעשה בתלמי המלך שכנס ע"ב זקנים והושיבם בשבעים ושנים בתים ולא גלה להם על מה כנסם. נכנס לכל אחד ואחד מהם אמר להם, "כתבו לי תורת משה רבכם." נתן המקום עצה בלב כל אחד ואחד והסכימה דעתן לדעת אחת וכתבו לו [כל אחד ואחד] תורה בפני עצמו. וי"ג דבר שינו בה, ואלו הן: "אלקים ברא בראשית" וכו' ע"ש
An incident occurred with five elders who wrote the Torah in Greek for Ptolemy the king, and the day was as difficult for [the people of] Israel as the day that the [golden] calf was made, for the Torah could not be translated sufficiently.
A further incident occurred with Ptolemy the king when he gathered seventy-two elders and placed them in seventy-two houses and did not reveal to them why he had gathered them. He went in to each one of them and said to them, “Write for me the Torah of Moshe your teacher.” God placed counsel into the heart of each one and their opinions all came to the same opinion and each one wrote for him his own Torah. They made thirteen changes in it, and these are: “God created in the beginning” etc.The second incident appears to be the same incident as the one described in the Talmud. Rabbi Yakov Emden (1698-1776), in his notes on Mesechta Sofrim, comments on the first incident, "נ"ל שזהו בן לאגע" – “It appears to me that this is [Ptolemy] son of Lagos”, referring to Ptolemy Soter, the first of the Greek kings of Egypt, and on the second incident he writes, "זהו פילאדילפו" – “This is Philadelphus”, the son and successor of Ptolemy Soter.
However, in his notes on Megillah 9a, Rabbi Emden appears to directly contradict this. He comments:
אין זה בטלמיוס פילאדילפו שידוע שהיה אוהב ישראל ובקש ההעתקה הידועה מהכ"ג שבירושלם בהכנעה ובהתרפס לו ברצי כסף ודורונות גדולות שעשה לבהמ"ק ולכ"ג ולזקנים מעתיקי התורה שתנתן לו בקשתו זאת כמפורסם בספר אריסטיאה שחובר על זאת באותו פרק המעשה ע"י המשולח של המלך לירושלם, אלא תלמי אחר הוא זה.
This is not Ptolemy Philadelphus, for it is known that he was a lover of Israel and that he sought the famous translation from the High Priest in Jerusalem with humility, humbling himself before him with appeasements of silver and great gifts made for the Holy Temple, the High Priest, as well as the elders who translated the Torah, so that they should grant this request of his. This has been made well-known in the book of Aristeas that was written on this topic by the emissary of the king to Jerusalem. Rather, this is a different Ptolemy.
In this comment, Rabbi Yakov Emden relies upon the Letter of Aristeas. The Letter of Aristeas tells us a story of how Ptolemy Philadelphus, in his desire to complete his great library in Alexandria, sent a letter to Elazar the High Priest  requesting his aid in collecting six elders from each of the twelve tribes (thus, seventy-two elders) to translate the Torah. To demonstrate his sincerity, Philadelphus first ransomed over one hundred thousand Jewish captives who had been enslaved during the reign of his father, Ptolemy Lagos. He also sent rich gifts of precious metals and works of art to the High Priest and the Holy Temple. According to the Letter of Aristeas, the elders knew why they were traveling to Egypt and they worked together as a committee in the translation. The Letter states:
Three days later Demetrius took the men and, passing along the sea-wall, seven stadia long, to the island, crossed the bridge and made for the northern districts of Pharos. There he assembled them in a house, which had been built upon the sea-shore, of great beauty and in a secluded situation, and invited them to carry out the work of translation, since everything that they needed for the purpose was placed at their disposal. So they set to work comparing their several results and making them agree, and whatever they agreed upon was suitably copied out under the direction of Demetrius. ...They met together daily in the place which was delightful for its quiet and its brightness and applied themselves to their task. And it so chanced that the work of translation was completed in seventy-two days, just as if this had been arranged of set purpose.
The miraculous agreement of the different translations is entirely missing from the Letter of Aristeas. Interestingly, Philo, who appears to base his story primarily on the Letter of Aristeas and perhaps local Alexandrian tradition, does include the miracle. He writes (Life of Moses II, VII):
Therefore, being settled in a secret place ... they, like men inspired, prophesied, not one saying one thing and another another, but every one of them employed the self-same nouns and verbs, as if some unseen prompter had suggested all their language to them. And yet who is there who does not know that every language, and the Greek language above all others, is rich in a variety of words, and that it is possible to vary a sentence and to paraphrase the same idea, so as to set it forth in a great variety of manners, adapting many different forms of expression to it at different times. But this, they say, did not happen at all in the case of this translation of the law, but that, in every case, exactly corresponding Greek words were employed to translate literally the appropriate Chaldaic words, being adapted with exceeding propriety to the matters which were to be explained; for just as I suppose the things which are proved in geometry and logic do not admit any variety of explanation, but the proposition which was set forth from the beginning remains unaltered, in like manner I conceive did these men find words precisely and literally corresponding to the things, which words were alone, or in the greatest possible degree, destined to explain with clearness and force the matters which it was desired to reveal....
On which account, even to this very day, there is every year a solemn assembly held and a festival celebrated in the island of Pharos, to which not only the Jews but a great number of persons of other nations sail across, reverencing the place in which the first light of interpretation shone forth, and thanking God for that ancient piece of beneficence which was always young and fresh. And after the prayers and the giving of thanks some of them pitched their tents on the shore, and some of them lay down without any tents in the open air on the sand of the shore, and feasted with their relations and friends, thinking the shore at that time a more beautiful abode than the furniture of the king's palace.
The story told by the Letter of Aristeas is quite different from the story told in the Talmudic sources, but Rav Yakov Emden nevertheless believes the Letter of Aristeas to be basically reliable. He therefore concludes that the translation story told in the Talmud and the story told by the Letter are two separate incidents. This is a difficult conclusion to accept, as it forces us to assume that there were two separate incidents in which a king named Ptolemy had a group of seventy-two sages translate the Torah. Most sources appear to disagree with this conclusion and maintain that the story in the Talmud took place with Ptolemy Philadelphus, and the Letter of Aristeas is simply inaccurate.
The Letter of Aristeas indicates that the Jewish community of Alexandria welcomed the translation as a great benefit, and this opinion is confirmed and repeated by Philo. The opinion of the Sages, however, appears to have been quite different. The events of the translation are not described as positive events. On the contrary, as we already saw, in Mesechta Sofrim, that an earlier translation was described as being "as difficult for [the people of] Israel as the day that the [golden] calf was made." Similarly, in Megillas Taanis (Maamar Acharon) it states:
בח' בטבת נכתבה התורה יונית בימי תלמי המלך והחשך בא לעולם שלשת ימים
On the eighth of Teves the Torah was written in Greek in the days of Ptolemy the king and darkness came to the world for three days.
The Septuagint had the obvious effect of bringing Jewish and pagan thought much closer together, but this proved a curiously one-way traffic. The translation was supposedly devised to persuade the Greeks of the correctness of Judaism, but its influence in this direction was negligible or non-existent…. But for the Alexandrian Jews it fulfilled an enormous role. It became, in fact, their Bible, in place of the Hebrew Bible which most of them could not understand.This event is therefore one of the tragedies which we mourn on the fast of Asara B’Teves, and it is mentioned in the Selichos of that day.
 Ptolemy II Philadelphus was the Greek king of Egypt from 283 BCE to 246 BCE. He was the successor of his father, Ptolemy Soter, the founder of the Ptolemaic dynasty, who had been one of Alexander the Great’s generals. During this period, the land of Israel was under the rule of the Egyptian Greeks. The Syrian Greek Seleucid empire took control of the land of Israel later.
 Literally, “seventy”, the Septuagint is sometimes referred to as the LXX, the Roman numerals for seventy. It should be noted that, despite the name, the Septuagint that we know of today is not the original translation made by the Sages. It is likely that the translation of the Sages was the earliest version of the Septuagint, which, over the centuries was repeatedly edited, modified, and expanded (from just the Pentateuch to the entire Jewish Scriptures and even some Apocryphal works).
 The significance of these works is that they were all written before the compilation of the Talmud. These sources are, therefore, not simply repeating the account told in the Talmudic sources. I would stress that this does not mean that the accounts in these works are therefore more reliable than the Talmudic sources.
 While ancient sources appear to have taken the Letter of Aristeas at face value, most modern scholars believe that the Letter of Aristeas was written at a somewhat later period by a Jew, probably from Alexandria. A middle position is taken by Victor Tcherikover, who, in his Hellenistic Civilization and the Jews (p. 274) writes “the document is basically genuine, but has probably been worked over here and there and by a Jewish forger.”
 One important source that discusses this topic in detail is Me’or Enayim by Rabbi Azariah Min Ha’Adumim (dei Rossi) (1514-1578). Unfortunately, I am not yet familiar with his discussion of this topic.
 For example, when translating the first verse of the Torah, the translators put the name of God at the very beginning of the sentence, “God created in the beginning.” The concern was that a more literal translation, “In the beginning, created God,” could be misunderstood to mean that God had been created by a prior being called “In the Beginning.”
 Rabbi Eliyahu Kitov, in his Sefer HaTodaah (Book of Our Heritage), Teves, has an interesting explanation of this analogy. He explains that just as the golden calf was thought, by its worshippers, to be a genuine intermediary with God, but was actually meaningless, so too, the non-Jewish readers of the Greek translation of the Torah thought that it was a genuine representation of the Torah, but it was actually entirely empty of the essence of the Torah.
 The existence of earlier, flawed, translations of the Torah is also mentioned towards the end of the Letter of Aristeas, where it describes the king’s reaction after having the completed translation read to him:
The whole book was read over to him and he was greatly astonished at the spirit of the lawgiver. And he said to Demetrius, 'How is it that none of the historians or the poets have ever thought it worth their while to allude to such a wonderful achievement?' And he replied, 'Because the law is sacred and of divine origin. And some of those who formed the intention of dealing with it have been smitten by God and therefore desisted from their purpose.' He said that he had heard from Theopompus that he had been driven out of his mind for more than thirty days because he intended to insert in his history some of the incidents from the earlier and somewhat unreliable translations of the law. When he had recovered a little, he besought God to make it clear to him why the misfortune had befallen him. And it was revealed to him in a dream, that from idle curiosity he was wishing to communicate sacred truths to common men, and that if he desisted he would recover his health. I have heard, too, from the lips of Theodektes, one of the tragic poets, that when he was about to adapt some of the incidents recorded in the book for one of his plays, he was affected with cataract in both his eyes. And when he perceived the reason why the misfortune had befallen him, he prayed to God for many days and was afterwards restored.
 According to the Letter of Aristeas, Aristeas was one of the emissaries that Ptolemy sent to Jerusalem.
 Rabbi Emden repeats this conclusion in his commentary on Megillas Taanis, Maamar Acharon. In his comments there, Rabbi Emden adds that, while Philadelphus wanted a proper translation, the coercive Ptolemy in the Talmudic version demanded a literal word-for-word, translation. This is why a miraculous correspondence between the seventy isolated translators was necessary.
 Josephus (Antiquities XII:2:5) says that this was the brother of Shimon HaTzadik.
 Philadelphus’ librarian.
 Philo refers to the Hebrew language as Chaldaic (also called Aramaic) possibly related to the use of the term Ksav Ashuris. (See the introduction of A. Kahana’s Hebrew edition of the Letter of Aristeas.)
 A similar insight is made by Rav Yerucham Levovitz in Daas Torah, Naso (7:12). He says that, although this was certainly a miracle, the incident also demonstrated the power of שכל ישר – straight (i.e. clear and undistorted) intelligence. Thus, all 72 sages understood the circumstances correctly and came to exactly the same conclusions.
 As noted previously, even Rabbi Yakov Emden’s own comments on Mesechta Sofrim disagree with this conclusion. It is possible that Rabbi Emden changed his mind on this matter at some point.
 Probably out of a desire to give a kinder portrayal of Ptolemy Philadelphus.
 However, an argument might be made that this statement was applied only to that early translation because of its imperfections, “for the Torah could not be translated sufficiently”, and does not apply to all translations.
 With the exception of Rabbi Yakov Emden, it seems that the dominant opinion is that this is referring to the translation under Ptolemy Philadelphus.
 The meaning of these three days of darkness is not clear. Shalsheles HaKabala (cited in the Tosfos Chadashim on Megilas Taanis) says that the Jewish people fasted for three days out of fear, as in the days of Haman, and “their faces blackened.” See the Chasam Sofer (Toras Moshe AH”T, Shemos) for a deeper explanation.
 The History of Ancient Israel (p. 203)
 Rabbi Aryeh Leib Gordon (19th century) makes the same point in his Iyun Tefila commentary on the Selichos of Asara B’Teves (printed in Siddur Otzar Tefillos).