Travertine is formed in hot springs and/or limestone quarries. It is formed by the precipitation of calcium carbonate. In other words, a chemical soup very high in concentration of calcium carbonate precipitates off the liquid and the remaining chemical soup hardens and is compressed into the travertine stone we have today. Kind of like a natural concrete in that you have a soupy mixture that hardens.
Travertine, has been used in design and architecture for centuries. This stone is recognisable in some of the world’s most famous structures including The Coliseum in Rome, the Basilique Du Sacre Coeur in Paris and The Getty in Los Angeles.