Why do you think manholes are round in shape?
(You need to think a little crooked for this )
If the manhole corresponded to any shape other than a round shape, then it will have a diagonal that is larger than the largest side, and the cover can fall in through the hole.
The round shape of the manhole, having a fixed diameter prevents this from occurring.
Edited on September 23, 2023, 1:19 am