Please note that 'millennium' is spelt with two 'n's. Please note also that the 2nd Millennium will not be complete until the END of the year 2000. The origin of the Gregorian calendar is 1 Jan AD 1. Add 2000 to get the start of the 3rd Millennium, i.e. 1 Jan 2001.
There is no year Year Zero in the conventional BC/AD method of dating because the concept of zero (and the so-called Arabic numerals) did not appear in Europe until about 500 years ago. The Gregorian calendar was set up using Roman numerals and without that wonderful Indian invention. ZERO. Ian Elliott Dunsink Observatory, Dublin 15, Ireland.
