Just a note for the eager digger ..
I attended a lecture a few years back concerning the "Black Death" and it's effects on the population.
One thing of note was that it seemed to be a practice to cover some of the pits in a broken "green on white" china as a marker not to disturb the area if digging in the future. (As the fear of "disturbing" the unknown disease still loomed).

Anyhow ... On the subject,

'Black Death' Skeletons Found Under Crossrail

Gary J.