i dont know much but the easiest way i could think of to make that would make curves in the half moons all over the place to kind of mimic where the arches are in that picture and make a lot of them and then make a nurbs square and then select a curve and then shift select the nurbs square and extrude using the tube option for extrude and make a nurbs surface.
then scale each end of the newly formed arch

hope this helps in the least