Why is "-ber" the suffix of the last four months of the year?

Question

• September
• October
• November
• December

Presumably something Latin, but my (admittedly brief) search sees only mention of the number-based root words.

More specifically, what does "-ber" mean?

Answer 1

From Etymonline:

The -ber in four Latin month names is probably from -bris, an adjectival suffix. Tucker thinks that the first five months were named for their positions in the agricultural cycle, and "after the gathering in of the crops, the months were merely numbered."

If the word contains an element related to mensis, we must assume a *decemo-membris (from *-mensris). October must then be by analogy from a false division Sep-tem-ber &c. Perhaps, however, from *de-cem(o)-mr-is, i.e. "forming the tenth part or division," from *mer- ..., while October = *octuo-mr-is. [T.G. Tucker, "Etymological Dictionary of Latin"]

Answer 2

Romans spoke Latin. Their first 10 numbers were: Unus, Duo, Tres, Quattuor, Quinque, Sex, Septem, Octo, Novem, and Decem. The Latin ber translates to per. This could be referencing a ratio. So Septem ber would be the seventh part of a ten month year of campaigning.

Their calender would then be Unusber, Duober, Tresber, Quattuorber, Quinqueber, Sexber, September, October, November, December for the 10 months they would be able to engage in war. Two months were added to the end of their calendar: January and February for the period where they wouldn't go to war.

Their calendar began with Unusber (named March) as their focus was on being able to conquer the known world.

January was named for the Roman god Janus, protector of gates and doorways. Janus is depicted with two faces, one looking into the past, the other into the future. January was meant to be a time when the military campaigns ceased and there time for peace and reflection.

February comes from the Latin word februa, “to cleanse.” The Roman calendar month of Februarius was named for Februalia, a festival of purification and atonement that took place during this period.

Unus ber was called March, named for the Roman god of war, Mars. This was the time of year to resume military campaigns that had been interrupted by winter. The word march is a play on this relationship, as one would march off to battle. March was also a time of many festivals, presumably in preparation for the campaigning season.

Duo ber became April, from the Latin word aperio, “to open (bud),” because plants begin to grow in this month. In essence, this month was viewed as spring’s renewal.

Tresber was named May for the Roman goddess Maia, who oversaw the growth of plants. Also from the Latin word maiores, “elders,” who were celebrated during this month. Maia was considered a nurturer and an earth goddess, which may explain the connection with this springtime month.

Quattuor ber became June, named for the Roman goddess Juno, patroness of marriage and the well-being of women. Also from the Latin word juvenis, “young people.”

Quinqueber became July, named to honor Roman dictator Julius Caesar (100 B.C.– 44 B.C.) after his death. In 46 B.C., Julius Caesar made one of his greatest contributions to history: With the help of Sosigenes, he developed the Julian calendar, the precursor to the Gregorian calendar we use today.

Lastly, Sex ber became August, named to honor the first Roman emperor (and grandnephew of Julius Caesar), Augustus Caesar (63 B.C.– A.D. 14). Augustus (the first Roman emperor) comes from the Latin word “augustus,” meaning venerable, noble, and majestic. The Gregorian Calendar then shifted the month of January to the beginning of the Year, which was fitting, due to Janus being the god of beginnings.