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(January 2007)| The oldest dating systems were in regnal years,
and considered the date as an ordinal, not a cardinal number.
For example, a monarch could have a first year of rule, a second
year of rule, a third, and so on, but a zero year of rule would
be nonsense. Applying this ancient epoch system to modern
calculations of time, which include zero, is what led to the
debate over when the third millennium began. Reckoning in
various cultures  In ancient times, calendars were counted in
terms of the number of years of the reign of the current
monarch. Reckoning long periods of times required a king list.
The oldest such reckoning is preserved in the Sumerian king
list. In England, and later the United Kingdom, until 1963, each
Act of Parliament was defined by its serial number within the
session of parliament in which it was enacted, which in turn was
denoted by the regnal year or years in which it fell. (See
Regnal years of English monarchs.) In C