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Moving back as far as the Roman times, in ancient Rome Man has started using stone to protect drain covers. The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and images of spies/heros using http://www.doctorant-marketing.com/blog/view/186907/a-channel-drain-trench-drain-is-a-type-of-floor-drain-that-has-a-channel-shaped-body-characterized-by-its-long-length-and-narrow-width popping out of manhole cover in Hollywood films appear. Historically ever since Man invented the sewage system since the Roman Times to drain water and urban waste away for sanitation purposes, manhole covers (drain covers or grates as we would prefer to call them) have been invented out from the necessity 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 current day, the sewage system is still being employed under all cities all over http://dolmush.com/wordpress/members/browningwesth94/activity/15923/ . As opposed to the crude stone manhole covers the Romans use in the ancient days, we now have special steel reinforced stone gratings that serve the thousand year old function of covering the inlets of our sewage system. A lot more than a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates