Obelix got bored, mystery solved.
Particle accelerator.
Cool. FWIW, I think you mean sheer enormousness. Enormity means great evil.
Walls are either built to keep something in or to keep something out. I would guess they might provide a barrier to chariots. According to wiki “The horse drawn wheeled vehicle probably originated in Mesopotamia about 3000 BC”
Loosely connected. Ylvis has serious questions about the history of Stonehenge. NSFW lyrics https://www.youtube.com/watch?v=mbyzgeee2mg
Dammit. Too slow… 
Enormity doesn’t mean what you think it does. The word you want is size.
Good idea. The wall could have also been covered with degradable material- like thorny brush or pointed sticks and such. But it doesn’t explain why the desire for such symmetry.
I think there is a spiritual component. Circle of life?
(and @old_editor)
From the definition you linked:
Great size. The quality or state of being huge : immensity the inconceivable enormity of the universe
What about these circles is not of great size, or enormity if you will?
perhaps it is where god set down his coffee cup?
(disclaimer: I only believe one of those two things [god/coffee] exists)
edit: as far as I’m aware, god’s coffee is available as a band name, feel free to use it, just don’t suck, I’d hate it if anyone blasphemed coffee.
Man, those ancient people had a lot of idle time, huh? And me, with all the social division of labor, can’t even catch a movie during weekdays.
It was supposed to be 18’ high, but some jerk wrote the order as 18".
I’m going to guess it’s also the one you worship…
I hate to be the downer, but 2000 years ago is not a very long time. The walls were built by people who had steel tools (invented in nearby Turkey 2000 years before that) and had the help of Pythagoras (500 years prior) and Euclid (300 years prior) for planning geometric earthworks. Not that you really need either to draw a circle: just a stick and a long rope.
It’s rather large to be a useful corral. The most important thing in the middle east when it comes to civil engineering is water. If, as it appears, the center of the circle is slightly elevated, I’d guess it was a rainwater retention system.
Another great guess. But I still don’t see the need for a perfect circle, as much of the length would be unnecessary. A damn or two located at the runoff locations would be much simpler.
The central hill location could simply be to help managing the rope easier? Could also be helpful for defense, if that was needed.
It looks pretty flat there to me; there are likely no good places to dam. Plus, a circle encloses the maximum area for a given perimeter.
If you want to contain runoff around a hill, or in a flat place, then a circle is the best option (lacking complex computers and laser-guided levelers as are used in modern rice paddies). If it’s a defense then it would be built to defend something, which seems unlikely for a random patch of ground. And the people of that area were building serious fortifications thousands of years prior to that.
My main concern with the article and writeup is the whole, “How mysterious that people a long time ago managed to stack stones on top of one another! Surely they were helped by aliens!”
“sheer enormity would have required extensive planning.”
Compared to most engineering of the period it would have been considered fairly trivial. This is no where near as large or complex as a roman road, and ~2.5 kilometers long. Not exactly the Appian Way (312 BCE).
you guessed right, it’s coffee! 
Interesting. To me, it clearly looks like water drains down the left side and exits the bottom of the picture. Then a smaller one on the right side.
