Going back as far as the Roman times, in ancient Rome Man has started using stone to cover drain covers. abc
The layman term for shower channel drain (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 ever since 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 avoid people from falling into underground sewage as well as 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 being employed under all cities all over the world. Rather than the crude stone manhole covers the Romans use 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.
More than merely a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates