Travertine originates from a mineral rock called tufa. It is a monomineral sedimentary rock built of calcite. It is formed around cold sources by the extraction of calcium carbonate from saturated calcium bicarbonate. The main characteristics of travertine are its durability and resistance to meteorological and other external factors. These characteristics were recognized several millennia ago, so that ancient builders used it to build very permanent buildings, churches and bridges, for example. Roman Colosseum.