My answer to a question Blood and Bone China asked on Facebook…

Q: Where does the myth about not being able to see a vampire’s reflection in a mirror come from?

A: The vampire is deemed not to have a soul, and hence no mirror will reflect him or her. The idea probably came originally from the prehistoric association of pools with sacred deities that were deemed to inhabit them, a widespread belief testified to by abundant votive offerings found by archaeologists at the bottom of ancient pools and ponds in the UK and Europe. Reflections seen in such places were thought to be reflections of the soul, not of the actual body, and hence to pose a danger of seduction. This could be either a danger of self-love (seen in the myth of Narcissus, etc), or a danger of the person’s soul being “taken under” by the watery deity. Possibly this had a root in a belief that one had to shed one’s selfishness when approaching such places, or risk calamity. Then, when mirrors came along in the Bronze Age, these would have been seen as having the similar capability to ‘steal’ or “embody” one’s soul, in much the same way as the similarly reflective dark watery pool. Modern tribal peoples often have similar beliefs, even today, about mirrors and camera lenses and their potential to “steal” one’s soul. As David Jones says, there are also several mirror folk beliefs around funerals and souls (i.e.: cover mirrors while laying out the dead body in a home) that have persisted to the modern day in certain places. The folk association of “bad luck” with breaking household mirrors probably also dates back to such antiquated beliefs. All these can be traced to the idea that the reflection in a mirror is that of the soul, not of the body.