October (Roman month) did not number days of a month sequentially from the 1st through the last day. Instead, they counted back from the three fixed points of the month: the Nones (5th or 7th), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Nones of October was the 7th, and the Ides was the 15th. The last day of October was the "pridie Kalendas Novembris," "day before the Kalends of November". Roman counting was inclusive; October 9 was "ante diem VII Idūs Octobris", "the 7th day before the Ides of October," usually abbreviated "a.d. VII Id. Oct."
September (Roman month) to the period August 19 to September 17. The Romans did not number days of a month sequentially from the first day through the last. Instead, they counted back from the three fixed points of the month: the Nones (5th or 7th, depending on the month), the Ides (13th or 15th), and the Kalends (1st) of the following month. The Nones of September was the 5th, and the Ides the 13th. The last day of September was the "pridie Kalendas Octobrīs," "day before the Kalends of October". Roman counting was inclusive; September 9 was "ante diem V Idūs Septembrīs", "the