The carpeting of Rome is cobblestones. Those square, chiseled blocks of volcanic rock are as important to the city's look and feel, especially beneath one's feet or the tires of a taxi, as the travertine and marble. (There are, however, rumblings -- sorry for the pun -- that replacement cobblestones are coming from China or Vietnam and not the hills around Rome). They are sometimes called Sampietrini, "little St. Peter's" because it was Bernini's piazza in front of St. Peters where the first black forest of cobblestones were planted. In the way the view to St. Peter's locates you in the city, the cobblestones are bumpy reminders of the "eternal city." Hated by many (car drivers in particular), they are beloved for the tactile reminder that you walk upon layers and layers of history here.
And, in a way that gives a preservationist great joy, I have learned that there is research showing that walking on cobblestones can be good for your health, especially for older people.