Study Eruvin folio 3A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
a molded or protruding cornice [amaltera] crowning the entrance should not be effective in rendering an alleyway fit to carry within it if it is higher than 20 cubits, as the Sanctuary had a cornice, and even so it was 20 cubits high, and no more. As we learned in a Mishnah: Over it were 5 oak corn
The Talmud attempts to dismiss this difficulty: And, with regard to that Mishnah, what is the refutation? Perhaps when that Mishnah with regard to cornices was taught, it was taught with regard to the Entrance Hall, whose height was 40 cubits, and not with regard to the Sanctuary.
The Talmud responds: And what is the difficulty with that? Perhaps the design of the Sanctuary was like the design of the Entrance Hall. Just as there were cornices in one doorway, there were cornices in the other.
The Talmud returns to its question with regard to a cornice: Why then did R' Ile’a say that Rav himself said: If the width of a cross beam is 4 handbreadths, even if it is not sturdy, it renders the alleyway fit for carrying within it. And if it has a cornice, even if it is higher than 20 cubits,
Rav Yosef said: This halakha with regard to a cornice was not actually stated by Rav, but rather it is a baraita. Who, in fact, teaches that baraita? Perhaps it is not an authoritative baraita, and Rav does not have to accept what it says.