@jokerxhisoka
How do you know? I imagine there's any number of photos of the place, if the mangaka hasn't been there himself. He might have very well traced one. In fact he should have. Lots of unnecessary work otherwise.
Well, it's common and advisable for manga artists or artists in general to trace or draw from reference of real places unless we know architecture or have the ability to draw fictional cityscapes effectively and quickly (since this is a monthly issue manga)
And damn aren't Europe one of the best references for ancient architecture.