4 Ways of Looking at a Wall

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1. As a jigsaw puzzle
Using nothing more than stone hammers and persistence, Incan workers in the 1400s pounded these stones into irregular shapes to build the palace of Inca Roca in Cuzco, Peru. The remaining walls uphold the Incas' reputation for ingenuity: They were fitted together so precisely—without mortar—that even today, tourists are hard-pressed to find a seam wide enough for a sheet of paper. But what's more amazing, says Stanford University anthro¬pologist John Rick, is that the walls still stand after six centuries in the earthquake-prone Andes.