A lot of people asked me which technic I used to create curved walls on my Amphiteater in Nikaia Antipolis' MOC.
About this creation
I spent a lot of time studying the best way to create the feeling of a natural curved wall, and one night I found out the way with a very very simple technic, based on a very few quantity of simple elements (Bricklink descriptions).
First of all, we need some simple parts: 2x3 Bricks, 1x6x2 Arches, Hinge Bricks 1x4 Swiwel (or plates), 6x8 plates, 1x1 plates and the most important part Bricks Modified 1x2 Log (or Bricks Round 1x1, but I prefer the "Log")
Then, we have to decide the height of the pillars: we'll work here on a basis of 5 bricks height pillar
Add Arches upon the pillars
Here you can see the use of the "Log" Brick: just between every Arch
Detail of the "Log" Brick
As I said, you can use Bricks Round 1x1 instead of "Log" Bricks, but I prefer the first solution
Plates are added upon the Arches
The Plates are strenghtened with Hinge Bricks after you fixed the curve angle
The wonderful thing is that 1x3 Bricks can be perfectly fixed upon the plates, even if they are "curved"...
... so you are ready to build the new range of arches
In my Amphiteater I added arches under the plates, to renforce the structure...
I've never seen this before, but I did practically a dumbed down version of this in my Elvish city. I was having trouble figuring out how to get a plate on top without huge gaps, but your pictures seem to have very small holes in the floor.