Cinnabar has been known since ancient times as a great source of red pigment. Cinnabar has also been known since ancient times as a great source of poison, that poison being the element mercury.
Cinnabar is the number one source of elemental mercury, and though its toxic properties have been known, they didn't stop ancient and not so peoples from using it for everything from cosmetics to carvings to pigment. That deep red is just too lovely to pass up, even if it means a closer funeral. Mining the stuff was akin to suicide.
An ancient Chinese carving done with cinnabar.
“Cinnabar is the number one source of elemental mercury.”
Text from 1570 detailing how to distill cinnabar.
Mercury is a unique metallic element that is a liquid at room temperature.