A manhole cover is a removable plate forming the lid over the opening of a manhole, to prevent anyone from falling in and to keep unauthorized persons out.
Description
Since the era of ancient Rome, sewer grates made from stone have been used to keep people from falling into the sewage and to catch anything large that might otherwise fall in.
Manhole covers usually weigh more than 100 pounds (roughly 50 kg), partly because the weight keeps them in place when traffic passes over them, and partly because they are often made out of cast iron, sometimes with infills of concrete. Th...