The Greek Old Testament is commonly referred to as the Septuagint (from the Latin word for 70) or as the LXX. But why 70? The answer to this question lies in the legendary account of the circumstances surrounding the first Greek translation of the Hebrew Bible.
The story begins with the Letter of Aristeas. Most scholars believe this letter was written not in the third century B.C.E as a firsthand account of the translation process, but rather as a second century B.C.E. defense of the translation.
Is it acceptable to read Holy Scripture in a language other than Hebrew? This was the question of the day. Aristeas says, "Yes," and he grounds his answer in the extraordinary circumstances that occasioned the translation. Aristeas' story forms the substance of our understanding of the origin of the Septuagint, but the legend, according to Jobes and Silva, grew over time. The following summarizes their telling of how the legend developed.
2nd Century B.C.E.
Aristeas explains that the translation process was initiated by the Egyptian king Ptolemy. He wanted to add a Greek translation of the Hebrew Bible to the great library in Alexandria. Ptolemy had his librarian request that translators and manuscripts be sent from Jerusalem. The high priest in Jerusalem agreed and sent 6 men from each of the 12 tribes of Israel to Alexandria. So, according to Aristeas, there were 72 translators who worked on the first Greek translation, which encompassed just the first 5 books of the Hebrew Bible. The 72 translators worked for 72 days, and their work was such a success that the Jews asked the librarian to provide them a copy for use in their communities. A curse was pronounced upon anyone who tampered with their perfect translation.
The number which arises from Aristeas' story, then, is 72. So, why 70?
1st Century C.E.
Jobes and Silva comment, "Writers subsequent to the Letter of Aristeas add little information of substance" (36). With respect to the circumstances surrounding the original translation, Aristeas is our man. But our question is why LXX (70)? The answer to that question comes later, as the legend develops.
Philo was a prominent Jewish philosopher who lived in the first century. According to him, the translators worked independently of each other, yet produced the exact same translation. This is quite a leap forward. Not even two people working independently of each other would produce exactly the same translation, much less 72. Therefore, as the logic goes, God must have intervened. Philo taught that the LXX was divinely inspired just like the Hebrew original.
2nd Century C.E.
In Sefer Tora 1.8, a rabbinic writing found in the Babylonian Talmud, the number 70 first appears. Jobes and Silva consider Sefer Tora's 70 yet another attempt to justify the translation. There were 70 elders who went up Mt. Sinai with Moses (Exodus 24:1-2, 9-11), and God appointed 70 elders to receive a share of the Holy Spirit along with Moses, in order that they might faithfully govern the people (Numbers 11:10-25). So, the detail that there were 70 translators of the 5 books of Moses ties the Greek Old Testament into this tradition of divine inspiration.
The Greek Old Testament is referred to as the Septuagint or LXX in light of this tradition. 70 refers to the supposed number of translators involved in the original translation of the Pentateuch. According to Jobes and Silva, by the middle of the second century, "the seventy" (οι εβδομηκοντα) can be found in the writings of Justin Martyr, Irenaeus, Eusebius, and Chrysostom, who used the term to refer to the entire Greek Old Testament.