The original Roman calendar (year of Romulus) was a ten-month year based on agriculture. Until 153 BC, March was the first month of the year, and the forms septem-, octo-, novem-, and decem- made a lot more sense in naming the months. Additional changes came with the calendar reform of Julius Caesar in 45 BC.

First of October

Mensis October was
Month number eight in a
Year having ten;
Now such a name appears
But, just remember, it
Made sense back then.

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