Going back as far as the Roman times, in ancient Rome Man has started using stone to protect drain covers.

Moving back as far as the Roman times, in ancient Rome Man has started using stone to cover drain covers.
The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and pictures of spies/ What is a floor drain? using the underground sewage system popping out of manhole cover in Hollywood films appear.
Historically ever since Man invented the sewage system since the Roman Times to drain What is a floor drain? and urban waste away for sanitation purposes, manhole covers (drain covers or grates as we prefer to call them) have already been invented out from the basic need in order to avoid people from falling into underground sewage and to prevent large objects from entering the drains which cause choking which eventually can lead to flooding.
Fast forward to the present day, the sewage system is still being employed under What is a floor drain? . As opposed to the crude stone manhole covers the Romans used in the ancient days, today we 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