Origins of the Names of the Last 4 Months of the Year

Today is the 1st of the September. It is the 9th month of 2010. The other day I started thinking about the English spelling of the last 4 months of the year:

• Sept-ember
• Oct-ober
• Nov-ember
• Dec-ember

This intrigued me, for "Sept" is the French word for 7, "Oct" is clearly a prefix meaning 8, "Nov" stems from "novem" which is the Latin word for 9, and "Dec" clearly is associated with "Deca" which in the metric system means 10.

Definitely a pattern here.  But how come all of our months appear to be two short of their numerical order in our calendar year?  This I did not know but a little research revealed the answer!  I find it beyond interesting that the calendar we use today stems back to a decision made 2263 years ago!!!  Some things in life change but clearly others do not at all.