I was learning the first few chapters of Eyruvin, and I wondering which of the mishnas are the source (or inspiration more likely) for the idea of a string around an area that allows one to carry inside that area.
I would have thought that case of the caravan where they create a "wall" of three strings (1:10) would be the most analogous case, with the issue that as mentioned in the footnotes (it mentioned Eruvin 17b, but don't see where, but I see where it is in the Rambam Hilchot Shabbat 16:12 if I am reading it right) that one cannot enclose an area that has an empty area of size beit satyam (5000 sq amot).
It would seem to me that parks, and many other places probably (parking lots?) would fall under this category.
So in essence I have three questions:
- Is Eruvin 1:10 the source/inspiration for the eruv around towns that exist today?
- If so and if the issue of the beit satyam of "utensil-less space" is in the gemara, then how is this issue dealt with?
- If the issue is not brought up in the Gemara, then where does the Rambam get this idea?