Moving 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 ( floor furnace grate ) is manhole cover. Say "manhole cover" and pictures 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 urban waste away for sanitation purposes, manhole covers (drain covers or grates as we prefer to call them) have been invented out of the basic need to prevent people from falling into underground sewage and also prevent large objects from entering the drains which cause choking which eventually can cause flooding.
Fast forward to the present day, the sewage system is still utilised under all cities all over the world. As opposed to crude stone manhole covers the Romans used in the ancient days, nowadays 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 just a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates