There is a well known difficulty cited in the Ramban (Shabbos 57a and Eruvin 59a) regarding Rashi’s shita that one of the requirements of a reshus harabbim is that there has to be shishim ribo traversing the street. The Ramban questions from where does Rashi know the criterion of shishim ribo; there is no mention of this requirement in Shas at all (see also Ritvah, 59a; Magid Mishna, Shabbos perek 14:1 and Rivash, siman 405).
The following explanation will clear up this difficulty: The Meiri (Shabbos 6a) cites a passage that is not mentioned in our Gemara, “לפי שאמרו בכאן אין רשות הרבים בבבל.” The Ravyah (siman 201, p. 276) refers to a similar passage that is not stated in our Gemara, “אמר עולה אין דרך רשות הרבים בבבל.” The Gemara in Berachos (58a) states,”.אמר עולה נקיטינן אין אוכלוסא בבבל” The Gemara explains that אוכלוסא (multitudes) is not less than shishim ribo. In Meseches Berachos, Ulla maintained that there is no shishim ribo in Bavel (Babylonia) and according to this version of Meseches Shabbos, Ulla stated there is no reshus harabbim in Bavel either. Therefore, it’s logical to conclude that since there was no shishim ribo in Bavel there was no reshus harabbim as well. Rashi, when he stated that one of the requirements of a reshus harabbim is that there has to be shishim ribo traversing the street, probably based his conclusion on a similar manuscript of the Gemara as did the Meiri and the Ravyah.
Incredibly, there is a manuscript of Meseches Shabbos (6a) in the Vatican Library (Bibliotheca Apostolica, Ebr. 127; see facsimile below) that actually has these additional lines that are not printed in our Gemara, “אמ' עולה אין רשו' הרבי' בבבל אמ' רבה בר בר חנה ירושלים אילמלא דלתותי נעולות בלילה חייבי משו' רשו' הרבי." Furthermore, Rav Mordechai Yehudah Leib Zaksh provides a fascinating bit of information that in the Munich codex (Bayerische Staatsbibliothek, Hebrew MS. No. 95; see facsimile below) on the margins of this daf (Shabbos, 6a) near the place of the insertion of this phrase in the Vatican codex there is a faint Addendum note that, although illegible, starts with an "א" (for אמ' עולה) and has precisely enough words to have been the same inclusion as the Vatican codex. (The Munich codex, which was completed in 1369, is the only complete extant manuscript of the Bavli; see Raphael Nossan Nata Rabbinovicz, Dikdukei Sofrim, p. 9. According to Breslauer Jahresbericht, 1905, p. 28, the Munich codex was based on a mid-ninth century manuscript.)
This facsimile above of Meseches Shabbos (6a) from the Vatican codex (Bibliotheca Apostolica, Ebr. 127) includes the additional phrase from Ulla. Note the placement of the passage from Rabbah bar bar Chanah also in Meseches Shabbos 6a and not just in Eruvin 6b as it is in our edition of the Gemara.