‘It was taught in agreement with Rab’: All the roofs of a town constitute a single domain, and it is forbidden to carry objects up or down from the courtyards on to the roofs or from the roofs into the courtyards respectively; but objects that were in a courtyard when the Sabbath began may be moved about within the courtyard, and if they were at that time on the roofs they may be so moved on the roofs, provided no roof was ten handbreadths higher or lower than all adjoining roofs;
so R. Meir. The Sages, however, ruled: Each one is a separate domain and no object may be moved in it except within four cubits.
But a contrary story is told:
R. Judah related: It once happened that during a time of danger we carried a scroll of the Law from a courtyard into a roof, from the roof into a courtyard, and from the courtyard into a karpaf in order to read in it.
This was during the repressions following the Bar Kochba revolt (132-136 CE). Hadrian forbade such things as Torah study, Shabbat observance and circumcision. Obviously a wrenching time which led to the martyrdom of Rabbi Akiva and others.
These persecutions, which lasted until Hadrian’s death in 138 CE, forced those who wanted to maintain the traditions into hiding and subterfuge. Interestingly, the Rabbis looking back at this time respond:
They, however, said to him: A time of danger can supply no proof.
Even the heroism of the martyrs does not supply legal justification for normal times.