Modular design my friend.
My map's made from 9 similar cells.
One cell I made with 4 archways and one displacement.
After that, it's copy-paste.
The only trouble is making it look good.
And lighting, lighting takes damn long if you don't know what you're doing right off the hop.
Although it didn't take me six hours, it took me three at the absolute most.
I felt so dirty after working on this, I had to use vertex manipulation on the archways to get them on grid, resize them to make them fit which would throw it off grid.
Thanks to the displacements, it was leakier than broken faucet, so I encased the entire thing in a box and func-detailed everything else.
But hey, it looks nice.