The Gas Natural Building, also known as Mare Nostrum Tower, is an office skyscraper located in the La Barceloneta neighbourhood of the Ciutat Vella district in Barcelona, Spain.

The Gas Natural Building was designed by the architects Enric Miralles and Benedetta Tagliabue in the high-tech architectural style.

[1] It has an innovative and distinctive image, as the building has two lower horizontal glazed blocks protruding and cantilevered out from the main tower.

It is located near the seafront, and to the southwest of two other La Barceloneta skyscrapers, the Hotel Arts and the Torre Mapfre.

In 2019, Naturgy sold the Mare Nostrum Tower to Inmobiliaria Colonial.