Manholes are usually round, primarily because roundness is the best shape to resist the compression of the earth; covers are round because they are easier to manufacture than square or rectangular shapes, they are easier to move by rolling, and they can't fall into the opening.[5] 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).[6]
While lifting a manhole cover may appear straightforward, several challenges can arise. Over time, dirt, debris, and corrosion can entrap the lid, making it extremely difficult to remove. In urban settings, the build-up of grime can turn a simple task into a labor-intensive one. Occasionally, the cover may be stuck due to the rusting of the frame or the accumulation of cement or asphalt around its edges. Thus, workers must be prepared with various methods to loosen stubborn covers, often employing prying tools or applying lubricants to aid the process.