On the road to Fethiye (has a gallery of its own) you will come by Patara. I went there not for the beach (which is great) but for the antique city.

This is an example of how a vault will stay in place if you put the stones in the right order. Probably, as is the custom now, they first used a wooden scaffolding to set the stones in place, then took the scaffolding out and lo and behold, they stay put.