“What makes a wall?”
Talmudic discussions on this topic go on for pages, displaying equally impressive levels of creativity and precision. The rabbis detail materials, size, and construction techniques. They test the limits of their definitions by exploring extremes: What is the smallest possible wall? The tallest? Can we make a wall from a living animal?
The rabbis discuss wall construction at length with regard to building a sukkah. The same conversations—or ones that sound very similar—appear in their determination of what is needed to create an eruv, a physical boundary marker needed for the purposes of legally carrying on Shabbat.