Moving back as far as the Roman times, in ancient Rome Man has started using stone to cover drain covers. abc
The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and pictures of spies/heros using the underground sewage system popping out of garage floor drain in Hollywood films appear.
Historically from the time that 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 necessity to avoid people from falling into underground sewage and also to prevent large objects from entering the drains which cause choking which eventually can cause flooding.
Fast forward to the modern day, the sewage system is still in use under all cities around the world. As opposed to crude stone manhole covers the Romans used in the ancient days, now 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