The Roman Calendar Is Different From Ours

The roman calendar looks very fam lar to us in terms of the names of the months. But what is different is that the early calendar only has ten named months. How come it only had ten months and later on developed 12 than welwhere liar with because the months had vaguely the same duration of our month. And the orphaned 60 odd days that aren't coted for in those ten months? Well, various theories about that. Could the months have been longer? Is this somehow related to some kind of lunar calendar? We've kept those intae but to pronounce them properly in latin, actually should have said november and december.