In a dry canyon strewn with the ruins of a long-dead city, archaeologists have made a discovery they hope will help unravel one of the most tenacious mysteries of ancient Peru: how to read the knotted string records, known as khipus, kept by the Incas. At the site called Incahuasi, about 100 miles south of Lima, excavators have found, for the first time, several khipus in the place where they were used -- in this case, a storage house for agricultural products where they appear to have been used as accounting books to record the amount of peanuts, chili peppers,...