So, to set the background a bit. I'm writing a story that is an alternate history basically diverging midway through the 1st century BC: the roman empire falls. Here I am looking at a Germanic people that made its way to Eastern Europe (bordering the Black Sea — above Dacia). After about 10 to 15 centuries (equivalent to late middle ages), could the fortifications have evolved to the castles we generally see in fantasy settings?
I've looked at a bunch of castles and their history and it is difficult to find any traces of things left from the 1st century BC. There is a Dacian fortress from around that time but other than that, nothing much.
So with minimal magic (there may be dragons that serve as kinda siege weapons but their fire is minimal and they don't fly, so really they're just OP mounts), would castles have evolved like they did in our timeline with a motte and bailey type construction followed by fortified stone keeps? And what are the odds of this leading to fortified cities similar to what we see Minas Tirith to be like in Lord of the Rings? As in a big city with a lot of walls around and a keep on top with even more walls?