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Moving back as far as the Roman times, in ancient Rome Man has started using stone to cover up drain covers. The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and images of spies/heros using the underground sewage system popping out of manhole cover in Hollywood films appear. Historically from the time that Man invented the sewage system since the Roman Times to drain water and http://wiki.dsd.bz/index.php?title=What-is-a-French-drain-f for sanitation purposes, manhole covers (drain covers or grates as we would like to call them) have already been invented out from the basic need to prevent people from falling into underground sewage and also to prevent large objects from entering the drains which cause choking which eventually could lead to flooding. Fast forward to the modern day, the sewage system is still employed under all cities all over http://www.internetblackout.org/index.php?title=Jonite-Stone-Grate-m . As opposed to crude stone manhole covers the Romans use in the ancient days, today we have special steel reinforced http://www.proxvm.com/wiki/index.php?title=In-the-world-currently-only-Jonite-reinforced-stone-is-the-only-stone-material-tested-and-certified-according-to-the-BS-EN-Standard-a that provide the thousand year old function of covering the inlets of our sewage system. Far more than a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates