Why manhole cover are round

• A round manhole cover cannot fall through its circular opening, whereas a square manhole cover could fall in if it were inserted diagonally in the hole.
• Circular covers don’t need to be rotated or precisely aligned when placing them on the opening.
• A round manhole cover is easily moved and rolled.
• Human beings have a roughly circular cross-section.
• Round tubes are the strongest shape against the compression of the earth around them, so the cover of the tube would naturally be round as well.
• It’s easier to dig a circular hole.
• Round castings are much easier to manufacture using a lathe.

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