Topic summary
Manholes
Extracted from the Wikipedia article Manhole.
Construction
Manholes are usually round, primarily because roundness is the best shape to resist the compression of the earth; covers are also round because they are easier to move by rolling, and they can't fall into the opening. But in the United Kingdom they are nearly always square, or rectangular, in shape, at least at street level. Manholes can also be found in a triangular shape (e.g. in Cambridge, and surrounding villages).