The Milion stone. This stone is the remnant of a road marker, originally constructed to have a door facing four sides and a dome embedded on four sides.
This used to be the starting point of all roads reaching Constantinople.
The signs say:
1377 KM (to) Rome
2040 KM (to) Tehran
2502 KM (to) London
DCCXXIII Miles (to) Babylon. This is 723 “miles” (Roman miles) or 665 statute miles, or 1070 KM.