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?
Classical pronunciation (i.e. during Roman times) is always hard C. So, yes, Caesar would be pronounced "kai-sar" and Cicero "key-ker-oh"
And, yes, December would be pronounced with a hard C in classical pronunciation as well, like in decade (which shares a root--the latin for the number 10 is "decem," and December was originally the 10th month).
Again, if this was true why was it changed? When did the transition to softer c's become apparent?
It is difficult to generalise regarding Vulgar Latin (whence the modern Romance Languages), as it was (by definition) not a literary language, and because, this being the case, it was far from uniform. Having said this, palatalisation is an exceedingly common sound change, and it is one to which the 'c' which is pronounced /k/ in Classical Latin succumbs in many phonetic environments, or so we believe, in what we can reconstruct of Vulgar Latin. A precise timeline or geographic representation of that change, however, is simply too much to ask of a pre-modern unwritten vulgar tongue.