Robert Arthurs reports on Quora first seeing this wonder of medieval over-specialization on display in Vienna, Austria:

Lantern shield | From the blog of Nicholas C. Rossis, author of science fiction, the Pearseus epic fantasy series and children's book

Doesn’t it look awesome? Well, looks can be deceiving.

You see that small hole in the top region of the shield? That is where a soldier would put a small lantern so that he could see at night. It was their version of night vision! The shield even had a compartment to keep oil so the lantern could be used for hours on end.

How cool, right? Wrong. Very wrong!

As awesome as this thing looks, it was really quite useless in combat. The oil for the lantern would often leak out. In combat, it would spill out uncontrollably. The wearer would get his arm covered in very flammable liquid. This means that your cool medieval night vision would actually set the wearer on fire more often than not. While being on fire illuminates one’s surroundings quite nicely, it may not be the best way to wage battle.

Here is a video for those who are curious to find out more about it (skip to 2:30 if you’re in a hurry):