Hiding in an attic

Question

There's a few instances I've seen in the gemarra where there were meetings in an attic. Both that come to mind are with Rabbanan Gamliel, although I'm not sure if it occurs with others. One is the Mishnah that he had diagrams in his attic to test witnesses about the New Moon (Yachin there brings the following gemarra that this is where they accepted witnesses). The other is he formed a Beis Din in his attic to rule on the intercalation of the year (Rashi there says it was designated to be a location for a Beis Din)

I'm wondering why specifically an attic. Was that simply his office? Or was he hiding up there. I ask because I once heard that during the times of Chazal there was a decree against learning Torah, so they had to teach in hiding, namely in their attic. Is this true?

Edit: I found another example of something happening in an attic in Kesubos 50b, this time not involving Rabban Gamliel, rather a quote from an Amora.

דאמר רב יצחק בר יוסף בעלייה התקינו שיהו בנות ניזונות מן המטלטלין

As Rav Yitzchak bar Yosef said: When the Sages sat in the upper chamber to rule on certain halakhot, which they could not do in the study hall at that time due to persecution by gentiles, they instituted that daughters should be sustained from movable property in addition to land.

Note: the Sefaria translation mentions what I heard, that they had to hide in the attic due to persecutions. It's coming from Rabbi Steinzaltz commentary on that gemarra. I'm not posting this as an answer as I'd like an earlier source.

Answer 1

This is kind of an open lead. The following is either a proof for the assumption, or a source for the conflating of circumstances.

Sanhedrin 74a discussed the vote in an attic in Lod where it was decided which sins a Jew should give up their life for:

א''ר יוחנן משום ר''ש בן יהוצדק נימנו וגמרו בעליית בית נתזה בלוד כל עבירות שבתורה אם אומרין לאדם עבור ואל תהרג יעבור ואל יהרג חוץ מעבודת כוכבים וגילוי עריות ושפיכות דמים

Margolios Hayam there brings the Doros Rishonim stating that this vote took place during a time of shmad, persecution, and concerned how to act during that persecution.

There seems to be an assumption that a vote concerning this subject, taking place in a well known battlefront where Torah learning was outlawed, would take place secretly. The fact that the vote happened in what is commonly translated as an attic seems to sit well with this assumption.

See here as well where the author paints this idea very clearly.

If I may suggest a different approach.
This will still address why we find so many of these votes in attic Batei Dinim and not in a regular Beis Medrash. This will also perpetuate the assumption that some degree of secrecy was intended.

We find in Avoda Zara 35a the idea that the Rabbis in Israel when instituting new restrictions would not divulge their reasoning for a year so that people wouldn't disagree and not accept their ruling.

דאמר עולא כי גזרי גזירתא במערבא לא מגלו טעמא עד תריסר ירחי שתא דלמא איכא איניש דלא ס''ל ואתי לזלזולי בה 

(Presumably, once the practice caught on, individuals who didn't agree with the logic wouldn't stop practicing it just because they disagreed. Or once they accepted the practice, they would assume the Rabbis were correct and wouldn't go investigating the logic behind it.)

It is possible based on this to assume that much novel deciding of Halacha happened in private.

Answer 2

I haven't found anything specific about hiding, but we have two-story houses in Israel from the time of the first temple, and no reason to believe this construction fell out of practice by the time of the mishna. The Harvard Semitic Museum has an exhibit on houses of ancient Israel that shows a reconstruction of such a house -- livestock on the first floor, space for people on the second.

An uncited tamudic story in this post describes Rabbi Yehoshua helping a visitor up the ladder to his loft to sleep.

Looking to the Tanakh itself, we know that Yiftach was expecting an animal to come out of "his house" (related, and that the Shunamite woman made an upper-story room for Elisha.

If we're willing to consider another religion's texts for historical reference (obviously not religious), they have Jesus having a meal in an "upper room" of somebody's house.

I would reason (no sources) that the concern about hiding expressed in the commentary isn't about the first floor versus the second floor, but rather is about the beit midrash (public space) versus someone's house. And if you're going to be in someone's house, you naturally want to be somewhere comfortable -- and maybe not in the middle of regular household activity, if you're there to study torah or make halachic decisions. An upper story sounds perfect for that.