The Gemara relates that many of the specific laws regarding tefillin are halakhah le-Moshe mi-Sinai – laws taught orally to Moshe Rabbeinu when he was receiving the Torah on Mount Sinai. For example:
- Rav Hananel quotes Rav as teaching that the need for a base for the square tefillin, called the titura, is a halakhah le-Moshe mi-Sinai.
- Abayye teaches that the hollow area through which the strap of the tefillin is pulled, called the ma’abarta, ishalakhah le-Moshe mi-Sinai
- Similarly, Abayye teaches that the letter shin, formed in the leather or the tefillin shel rosh – tefillin worn on the head – is halakhah le-Moshe mi-Sinai.
- Rabbi Yitzhak teaches that the rule requiring the leather straps of the tefillin to be black is a halakhah le-Moshe mi-Sinai.
- A baraita is quoted as teaching that the requirement that tefillin must be square is a halakhah le-Moshe mi-Sinai
The Gemara suggests relating this last requirement with the law that appears in a Mishnah in Masechet Megillah (24b), which warns that wearing round tefillin is dangerous and will not fulfill the mitzvah. Rav Papa argues that the Mishnah inMasechet Megillah may be talking about a different case – where the tefillin were made round like a nut with no base and there is concern lest the individual wearing such tefillin may crack his skull if he bangs his head while wearing them. Thebaraita is teaching that the squareness of the tefillin is a requirement.
Although the requirement that tefillin be made square is clearly presented by the Gemara as a halakhah le-Moshe mi-Sinai, nevertheless, it appears from the discussion of the rishonim that this was only viewed as a necessity with regard to the tefillin shel rosh, but that the single parchment of the tefillin shel yad – tefillin worn on the arm – could be placed in a cylindrical leather covering if placed on a square base. Evidence of this practice can be found by examining the tefillinfound in the Cairo geniza and in other illustrated manuals from the Medieval period.
