Moving back as far as the Roman times, in ancient Rome Man has started using stone to cover up drain covers. abc
The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and pictures of spies/heros making use of 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 would prefer to call them) have been invented out of the basic need to prevent people from falling into underground sewage and to prevent large objects from entering the drains which cause choking which eventually may lead to flooding.
Fast forward to the present day, the sewage system is still utilised under all cities worldwide. As opposed to crude stone manhole covers the Romans use in the ancient days, today we have special steel reinforced stone gratings that provide 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