Roman pronunciation of the letter C and traditional month names.

So I've heard that Roman's had no 'soft' c's in terms of pronunciation. I.e Ceasar was actually pronounced Keaser/Kaisar/etc thus the German word Kaisar~. Was this accurate? If so, then wouldn't the traditional monthly names such as December be pronounced Dekember similarly to Decade? Just a quick inquiry. Again, if this was true why was it changed? When did the transition to softer c's become apparent?