I love the 'star fort' walls, those are very recognizable as inspired by historical maps I've seen. Looks like a vector to me? My suggestion to keep it looking historically correct would be to try get some 'lineart' textures to delineate certain aspects. Maps like these often had the echo water lines, which, in Photoshop, is super easy, and in Illustrator, is a HUGE pain.

Alternatively here's a looping water fill I recently made for a map commission to be historically stylistic if you wanted to fool around with it.

Click image for larger version. 

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Quite well done.