American Scientist

To the Editors:

The first sentence in Henry Petroski’s column “Machu Picchu” (Engineering, January–February 2008) reads: “The Inca people may not have had a written language, but the marvels of construction that they left behind continue to speak volumes about their engineering genius.” It is true that the Incas did not have writing based on units of sound. But in quipus (knotted, colored cords) they had writing based on units of meaning. This form of writing, called concept writing, is familiar, for example, in our choreography and mathematics. Moreover, quipu concept writing is eminently suited for planning and recording the types of constructions that Petroski admires.

Robert Escher
Ithaca, NY