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.
Knowing whether the traditional techniques for building reed boats were in use at the time Tiwanaku was inhabited would be most useful to know in order to evaluate the support for the archaeologists' hypothesis.