Dracosolon
Emperor
How about Alesia? It was a fortified Celtic town with impressive fortifications, and was the site of a major epic battle during the Gallic war, where Caesar besieged it.
It has a lot of cultural importance, nicknamed Caesar's military masterpiece and the last stand of Vercingetorix and Celtic resistance, plus I found some really nice recreation of it.
Could fit with the gameplay too, building this when defending from the romans, kind of like following the footsteps of Vercingetorix.