This is an old Roman arch, with a restaurant built around it (literally, part of the arch is inside the restaurant).  Thankfully, they had a little plaque outside explaining the history.  It was built around 1 BC and is thought to have been the city gate to the walls.  Or, perhaps as later excavations showed, an entrance to a holy site.  I like to think it was part of a holy site.  (taken 4.4.2015)