Caesar, from our tour group, films this interesting construct, while Heather and Margaret examine the entrance to a shop nearby.  The stone slabs were put in place to allow pedestrians to cross the street, avoiding the water which inevitably flooded the streets after a rainfall.  The spaces in the slabs are to allow the water to flow through, but more importantly, are spaced so as to allow chariot wheels to pass.  You can see the grooves worn in the stone by their passing.  Off to the left, you can find evidence of another fascinatig aspect of first century Roman architecture; the shops had sliding wooden doors which ran along grooves at the front of the store.