The later books of the Tanakh make it clear that one may not "carry burdens" on Shabbat. This is a recurring theme in the Book of Ezra.The rabbis of the Talmud record that the Oral Torah understands this as being the primary meaning of the Biblical injunction "let no man leave his place on the Sabbath day".(Exodus 16:29) That is, not to transport from a Private Domain to a Public Domain or carry within a Public Domain, on Shabbat. These distinctions date back to the encampment in the wilderness, where the Israelites camped in tent groups, which eventually formed into four "camps", each of three tribes, with a broad thoroughfare between the camps. For most of history this was the common situation in the Middle East, as well as in most other places. Houses were built around a central courtyard (chatzer). The courtyards opened into alley ways (mavo'ot). Alleyways would, in turn, enter into a broad thoroughfare which went from one end of the city to the other. This can be seen in Jerusalem's reconstructed "Cardo", as well as in old cities in Israel and Europe, Each house was a "Reshut Hayachid" (Private Domain), the broad thoroughfare was a "Reshut Harabbim" (Public Domain). Carrying an object from the Private to the Public Domain constitutes a Biblical prohibition, as does carrying a burden within the Public Domain. The courtyards and alleyways are called "Karmelit" (semi-public Domain), which is considered as Private in Biblical law, but as public in rabbinic law (this is a classical "fence around the Torah"). It is completely permissible to carry within a Private Domain.
It was felt in very early times that the Shabbat would be much more enjoyable if neighbors could get together and bring things from one home to another. Families could join together for celebratory meals and the like. A series of enactments were made to allow for this. One enactment was called "Eruv Chatzerot" (the combining of courtyards). Bread, either baked from dough contributed by each household in the courtyard, or donated to the entire population of the courtyard by one person, was deposited in a central place. Now, all the homes in the courtyard were surrounded by a wall, and the bread constituted a common kitchen, making all the homes in the courtyard into one! This is essentially similar to a single home with many rooms. It is still one Private Domain. The Talmud attributes this enactment to King Solomon, with a Heavenly Voice proclaiming G-d's delight "If you are wise my son, I will also rejoice!". G-d loves unity! Another enactment was made, extending the first one to all the courtyards in an alleyway. This is called "Shuttufei Mavo'ot" (combining alleyways). Each courtyard would contribute food (it may or may not be bread) into a central place, and a symbolic doorway would be made for the alleyway, partitioning it off from the Public Domain.
The question arises if the Eruv solution would work for the Public Domain as well, thereby uniting the entire city! Some said yes. Some said no. Some said a qualified yes. Since the main thoroughfare has a Biblical prohibition of carrying, could a rabbinic enactment undo this status? The Talmudic consensus is that it could only be done if the entrances to the Public Domain, that is, the city walls, would have doors that close at night. (Not uncommon in the Ancient East). Then it would cease being a true Public Domain, and an Eruv would be efficacious. There is an entire tractate of the Talmud devoted to the Eruv. it is one of the most difficult. But throughout the ages, the Eruv was of great benefit to the Jewish people, uniting communities into one (as is the ideal!).
Today, however, our cities are not built like that. Is an eruv even possible? Is it advisable? In the last thirty years, virtually every major Jewish community has constructed an eruv. Some celebrate this. Some see it as a tragedy and a travesty. Why? In every community with an eruv, some will refuse to use it. Why? That will be the topic of my next post.