No other city has anything like the number of porticoes or covered walkways found in Bologna. In the city centre there are barely any stretches of pavement not topped by an ornate, arched covering. The first porticoes were built out of wood, some thirteenth-century examples of which still stand. They proved so popular that by the fourteenth century construction of stone or brick porticoes, high enough to accommodate people on horseback, were compulsory on all new streets. Today, some 38km still stand, including the longest portico in the world, leading from the city up to the Santuario di San Luca.