Rav Nahman said not to be strict about anything. That is in terms of Jewish Law but also in terms of every day matters.
So for years I was not at all careful about carrying things in a public domain on Shabat. Sadly I can not learn Torah but I did get a chance to glance at a few pages in tractate Shabat and noticed that carrying is a big issue over there.
Even though you see the idea that a public domain in only where 600,000 people walk through in Rashi and Tosphot and the Shulhan Aruch of Rav Joseph Karo itself brings it. Still it does not seem to be in the Gemara itself. I even noticed in the Yerushalmi some incident where a sage accidental carried on Shabat said he would bring a sin offering when the Temple would be rebuilt.
How would that have been possible in Babylon? the Jewish cites there were minuscule. Just think about Rome at the peak of its power. It had about a million people. How could small Jewish towns have had comparable numbers?
