A Sukkah which is higher than 20 ammot high is not valid.
Why is this?
Rabha explained, it is written [Lev. 23:43]: “In order that your generations may know that I caused the children of Israel to live in booths.” Up to twenty ammot a man knows that he is living in a booth, but higher than twenty ells he does not know, because his eyes do not frequently perceive the roof.

Sukkot Chapter 1

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19 September in History

Israel launched its first satellite for secret military reconnaissance on this day 1988.

11 Tishrei in History

Today marks the passing of Mar bar Rav Ashi 466 CE.

It is also the day after Yom Kippur, when one should start to build their Sukkah in advance of the upcoming holiday which will be celebrated on Wednesday night of this week.