And Moses wrote all the words of the Lord
Jarchi says, all from the creation, to the giving of the law, and the commands at Marah; but though these were written by him, yet not at this time; but as Aben Ezra more truly observes, what are mentioned in this "parashah", or section, or what is contained in the two preceding chapters, he not only related to them from his memory, but he wrote them in a book, which is after mentioned, that they might be seen and read hereafter; for these were not the ten commands, they were written as well as spoken by the Lord himself, but the judicial laws before mentioned:
and rose up early in the morning:
not on the fifth of Sivan, as Jarchi, the day before the giving of the law, but on the eighth of that month, two days after it:
and built an altar under the hill:
under Mount Sinai, about the place where the bounds were set, beyond which the people were not to go:
and twelve pillars, according to the twelve tribes of Israel:
to answer to them, and which were to represent them, as seems by the following account; these probably were made of marble stone, of which Mount Sinai consisted, and of which there was plenty thereabout.
The Brenton translation of the Septuagint is in the public domain.