> Quintilis was renamed after Julius Caesar. Later Sextilis was renamed > after Augustus Caesar. It is often said that the month lengths were > changed at the same time, but at least one version of that story is > fabricated and there's a distinct lack of evidence for it. Other emperors > had months renamed after themselves too, but those names didn't stick. > There's no evidence that any of them was accompanied by changes in the > lengths of months either.
The Oxford Companion to the Year is pretty explicit about this in its chapter on the Roman Calendar. It says that before Julius Caesar: Ianuarius 29 Quinctilis 31 Februarius 28 Sextis 29 Martius 31 September 29 Aprilis 29 October 31 Maius 31 November 29 Iunius 29 December 29 The reason was most of the months had odd lengths because odd numbers were lucky, but to get the year to have an odd number of days you need one month to have an even number of days. There was a leap month system where Februarius was cut short and an extra month was inserted. After the reform: Ianuarius 31 Quinctilis 31 Februarius 28 Sextis 31 Martius 31 September 30 Aprilis 30 October 31 Maius 31 November 30 Iunius 30 December 31 They also explain where the extra days were inserted. They say Quinctilis was renamed Julius after he'd been murdered. Their entry for "30 February" notes: There is no truth in the assertion by some modern (but no ancient) writers that Julius Caesar gave all the odd months 31 days, February 29 days and 30 in a leap year, and all the even months (including Oct) 30, but that Augustus upsets the logical arangement in order to make his month of August as long as Caesar's July. Nevertheless, 30 February has existed three times in the calendars of particular countries: once in Sweden, twice in the Soviet Union. David.