There they faced two hardy tribes, the Soras and Rucanas, whom they besieged and overcame. About 1350 the Incas bridged
the Apurimac River and its immense canyon. It had previously been bridged at three different places to the southwest; but the
new suspension bridge built by the Incas crossed at the point which formed a straight line from Cusco to Andahuaylas and was
the Incas' largest bridge, 148 feet (45 meters) long. They called it huacachaca, ``the holy bridge.'' With this event the Incas
collided with the Chanca, a powerful, belligerent tribe which disputed the Apurimac passage. Toward the end of the reign of
Viracocha (died 1437) the Chancas made a surprise attack and invaded Cusco. Viracocha fled for safety to the Urubamba
Valley, but his son organized the defense of Cusco, and the Chancas were completely defeated.