Nebuchadnezzar was not a good guy, by Biblical standards. He was also unpleasant company for a few years when he came to believe he was a cow and ate grass. What caused this madness? It might have been how he chose to decorate his palace.
Rome was the first city on the planet to have an extensive and efficient municipal water system, thanks to the empire's ambitious aqueduct system that's still found throughout Europe. But that infrastructure was also pumping ancient Romans with lead—up to 100 times the amount of lead found in local spring water.
Ever since Neil DeGrasse Tyson mentioned the "lead in the water" theory of why Rome fell on Cosmos, scientists and historians have been tearing up the internet to explain all the problems with this idea.