This is a photo of the 'Via Principalis' of a Roman city of between 10 and 15,000 people now situated in eastern Romania near Constanta. It was the main East to West street in the city and this is a view from the city gate.
The tracks are designed for the wheels of carts and the gap between the tracks was for sewage. According to the (impromptu) guide, the tracks were deliberately set a certain width apart in order to ensure that only carts with axles of a certain width were able to safely use the Via - the width was the one that carts built in the city used. Carts from outside the city could not enter.
I love ancient ruins and this was an incredible huge city almost entirely excavated and no tourists at all. You can still see the main streets though, the agoras, meeting places, some basilicas built after Christianity. A pretty impressive place.