As I enjoyed my days off around New Year's, I wondered why the first of January started the year. It turned out this happened to be the day two Roman counsels were appointed and it stuck. I didn't realize this wasn't fully adopted until the 18th Century.

It shouldn't be surprising that the date went back and forth in the Western world as a result of religion. The Wikipedia entry for New Year's Day explains England's new year's history, which puts a different spin on why January 1st is the first day of the year:

Most countries in Western Europe officially adopted January 1 as New Year's Day somewhat before they adopted the Gregorian calendar. The Feast of the Annunciation, March 25 (9 months before December 25), was the first day of the new year in England until the adoption of the Gregorian Calendar in 1752. The March 25th date was called Annunciation Style; the January 1 date was called Circumcision Style, because this was the date of the Feast of the Circumcision, being the eighth day counting from December 25.