9 Answers

The desired and politically correct answer to the question is: "Manhole covers are
round because round is the only shape that can never fall ...KOTF   2012.

To fit round men?

I will surmise that because the " riser ".., the " Donut".., and all the pipes that the manhole gives access to.., are round.
Besides, when the cover needs to be lifted, a round one will allow easier removal than any other shape.
When you put any other shape on edge, the circle affords the least perimeter area in contact with the hole.., thus allowing the easiest removal.

Source(s):

30 years in construction

They are not round.Tennis balls are round.Manhole covers are circular.

The covers are round because the "manholes" are round.

So that they can't fall into the hole.Square ones could fall into the opening.......

because they are easier to roll off of the delivery truck than the first prototype, the oval manhole covers! 

          I like  the square ones too !!! LOL

Round is easier to make than other shapes and easy to set in place. Triangular and square were tried but were more difficult to produce and maintain. The belief in symbolic shapes has gradually faded into arts, skills and crafts.