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Uncovered 9 Facts About Manhole Covers

You've seen them your entire life, but how much can you say you know about manhole covers?

We uncovered a few little-known facts about these round objects providing access to a world of underground infrastructure.

9 Facts about Manhole Covers

  • 18 million manholes dot the surface of our country.
  • In the 1st Century A.D., Romans made the first manholes out of sandstone.
  • On older manhole covers, square pegs provided grip for horse hooves.
  • Today’s manhole covers are made of cast iron, concrete or both, and weigh about 110 pounds.
  • The oldest manhole cover in NYC is 150 years old.

Manholes are round for safety.

  • A round cover can’t fall down a round hole.
  • A square manhole cover, tilted on it’s side can, risking injury to anyone below.
  • Also, a round manhole cover has a smaller surface than a square one, so less material is needed to cast the cover, meaning less cost to produce.
  • Round manhole covers can be easily transported by rolling, and they don’t need to be rotated to align with the manhole.

A popular myth says a nuclear test in the 1950s created enough pressure to jettison a manhole cover out into space.