The Origin of Month Names

Date: 10/17/98 at 16:47:44
From: Courtney Waugh
Subject: History of calender

Dear Doctor Math,

If oct is the prefix for 8 and dec is the prefix for 10, why is October 
the 10th month and December the 12th month? When were the other two 
months added and why?  A relative told me that July was added for 
Julius Caesar but I don't know why.

Thank you,
Courtney Waugh

Date: 10/19/98 at 13:48:08
From: Doctor Peterson
Subject: Re: History of calender

Hi, Courtney, 

There are two parts to the answer. Two months were added, but adding 
them didn't change the numbering, and it happened long before Caesar. 
There were originally only ten months in the Roman year. The two that 
were added, in the seventh century B.C., were January and February. The 
ancient Roman calendar still started in March, however. Only later, in 
the second century B.C., was it changed to start in January.

As for Julius Caesar, he didn't add a month, but he changed its name. 
Before he and Augustus Caesar after him renamed months for themselves, 
those months (July and August) were named for their numbers. Here is a 
list of the months with names that came from their number:

    Roman name          Latin No.   No.
    ----------          -------     ---
    Quintilis (July)    Quinque      5
    Sextilis (August)   Sex          6
    September           Septem       7
    October             Octo         8
    November            Novem        9
    December            Decem       10

Here are two pages on the Web that tell more about this:

Roman Calendar (James Grout, SPQR: Encyclopaedia Romana)  
  http://itsa.ucsf.edu/~snlrc/encyclopaedia_romana/calendar/romancalendar.html

Calendopaedia - The Roman Calendar (Michael Astbury)
  http://www.geocities.com/CapeCanaveral/Lab/7671/roman.htm   


- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/