Places and monuments emphasized in tourism campaigns include: Old San Juan, promoting the historic nature of its colonial buildings and narrow streets covered by adoquine, a blue stone cast from furnace slag; they were brought over as ballast on Spanish ships. This includes the city's ancient defensive wall and forts, most notably El Morro and the Castillo San Cristóbal. On January 23, 1984 both of these edifices were catalogued as being part of humanity's cultural patrimony. The restaurants and art galleries in the zone are visited by tourists. The local universities are promoted as historic places, most notably the campus of University of Puerto Rico located in Río Piedras, which is the oldest university on the island being founded in 1903.