Going back as far as the Roman times, in ancient Rome Man has started using stone to protect drain covers. abc
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 since that time 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 prefer to call them) have been invented out from the basic need to stop people from falling into underground sewage and to prevent large objects from entering the drains which cause choking which eventually could lead to flooding.
Fast forward to Jonite Street Furniture , the sewage system is still being used under all cities all over the world. Instead of the crude stone manhole covers the Romans used 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.
Much more than a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates