Why, after setting 400 rights, does it not allow me to enter the directory?

Question

Xubuntu

I typed in the terminal:
sudo chmod -R 400 /var/www/html
after which I can’t enter the directory, it says: "Permission denied", the ll and ls commands give a similar result.
Why so, if I set the rights to read?
ps: I work as a user sas, the owner of the html directory is also sas

Answer 1

Because to view the directory you need to have execute access (x)

Answer 2

for ls, we need x more rights, in other words, we set at least 500, and preferably 700