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

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 manhole cover in Hollywood films appear.
Historically since that time Man invented the sewage system since the Roman Times to drain water and 8 inch drain cover for sanitation purposes, manhole covers (drain covers or grates as we would like to call them) have already been invented out of the necessity in order to avoid people from falling into underground sewage as well as to prevent large objects from entering the drains which cause choking which eventually may cause flooding.
Fast forward to the present day, the sewage system is still utilised under all cities around 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.
Far more than a cover, check out Jonite's range of drain covers (drain gratings) here: https://www.jonite.us/products/creative-grates