Tiwanaku's elites gained their status through the surplus food they controlled, collected from outlying regions, and then redistributed to the general populace. Further, this elite's control of llama herds became a powerful control mechanism, as llamas were essential for carrying goods between the civic centre and the periphery. These herds also came to symbolize class distinctions between the commoners and the elites. Through this control and manipulation of surplus resources, the elite's power continued to grow until about AD 950. At this time, a dramatic shift in climate occurred, causing a significant drop in precipitation in the Titicaca Basin, believed by archaeologists to have been on the scale of a major drought.