Some words of introduction to the tractate. The phenomenon of this loophole that allows us to carry - on the one hand, feels very permissive, and on the other hand, was limiting for the sake of keeping Shabbat. Also some technique and recommendation for managing the new tractate and its more extensive halakhic (rabbinic) discussion. Note that eruvin bring the community together. Plus: explaining the term, in the context of the several kinds of eruvin. And the different domains, in brief. Now, to the daf, with its opening mishnah: When an alley has 3 homes, that are united somehow, and open out to a public alley - you can't carry there, unless you add a crossbeam to essentially join those homes together. How high can that crossbeam be? The Gemara jumps in to compare the case and thereby find some answers, among comparable architectural areas of halakhah.