The ruins of the prehistoric Bolivian city of Tiwanaku feature green andacite stones weighing up to 40 tons  These stones were quarried at Copacabana, which is across a lake and about 90 kilometers away  Archaeologists hypothesize that the stones were brought to Tiwanaku on reed boats
To show this was possible, experimenters transported a 9-ton stone from Copacabana to Tiwanaku using a reed boat built with locally available materials and techniques traditional to the area
whether the traditional techniques for building reed boats were in use at the time Tiwanaku was inhabited