Good question, Paul;-
      BC Dates actually began in Britain during the Druidic period.
They wanted a way to tell time and dates so they built this big thing
with lintels and rocks and peepholes. They had to have a starting
date so one Memlic the Unbearable said, "I have had a vision in which
the spirits have told me that it is now 2345 BC. The way to tell the
date is to subtract a year every time the sun shows through this peep-
hole and onto the mark I have just made on that there rock."  So
that's what they did, knowing full well that when they ran out of
years, they would have a real electronic nightmare and they wouldn't
have to pay their phone bills.
     Art