In 2001, UNESCO approved the Convention on the Protection of the Underwater Cultural Heritage, which was ratified by Spain in 2005. According to this document, Underwater Cultural Heritage includes “all traces of human existence having a cultural, historical or archaeological character which have been partially or totally under water, periodically or continuously, for at least 100 years such as: sites, structures, buildings, artefacts and human remains, together with their archaeological and natural context; vessels, aircraft, other vehicles or any part thereof, their cargo or other contents, together with their archaeological and natural context; and objects of prehistoric character."