What you are seeing on the back is a grill. Peru, along with the USA, is one of the few countries that used grills to dissuade people from cleaning the cancels from stamps so that the stamps could be reused. The grill would cut the paper fibers whereby the ink from the cancel would soak into the broken paper fibers supposedly making it impossible to remove the cancel.
My Scott catalog (2008 Edition) shows this stamp as Illustration A17 Sun God of the Incas although the Stamp in question appears above the listing for 118 which is what confused me,
I guess Scott makes mistakes from time to time, the stamp I have is shown with no number