Divus Augustus, Ch. 100, Sec. 1 (my translation). If you’re wondering about the dates, the Romans had a very different (and complicated) method of identifying the days of the month. Basically, there are three measuring points in a month – the Kalends, the Nones and the Ides. In general dates were based on the number of days before or after these points. Augustus’ death, according to Suetonius, fell 14 days before the Kalends of September. Because the Kalends of September is the first day of the month, 14 days back (counting the Kalends as the first day) is August 19. Before 8 B.C.E., the month of August was named “Sextilis” as it was the sixth month in the 10 month Roman calendar. Sextilis was renamed August in honor of Octavian. They could have chosen a worse name. Much later, the Anglo-Saxons in England would name the month Weodmonað, meaning “weed month”.
The word “Kalends”, sometimes spelt Calends, is derived from the Latin Kalendae, which is derived from the Greek word, ?a?e??, meaning to call or announce (the priests would announce the new moon at the beginning of each month). The English word “calendar” has the same history.