Great Regulars: Indeed, the Gemara spends some time arguing

that the Tabernacle, which the Israelites built in the desert, and the Temple, which Solomon built in Jerusalem, are legally and scripturally connected, so that what applies to one also applies to the other.

Pragmatically, too, it's important for the crossbeam not to be more than 20 amot high. This is because the function of the crossbeam is to remind people that they are passing out of a private domain, the mavoi, and into a public one, the street; and if it is too high up, passerby may not notice it. In Eruvin 3a, the rabbis draw an analogy with the succah, where the same height limitation applies. In a succah, the covering or s'chach may not be more than 20 amot from the ground, because the whole point of the succah is to give the feeling of being in an enclosed structure.

from Adam Kirsch: Tablet: Navigating the Talmud's Alleys

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