Mura di Pisa

This guide to the Mura di Pisa opens with a question you can answer with your own eyes: why the stone underfoot shifts from grey to pink partway up the wall. It follows the order Consul Cocco Griffi gave in 1154 after Emperor Frederick Barbarossa rode through and exposed the city's vulnerability, and the crews who quarried grey limestone at San Giuliano before a later generation switched to reddish breccia from Asciano. You'll hear about the putlog holes still visible in the stone, sockets for the wooden scaffolding masons climbed without cranes or machines. Look along the wall for the color change as you walk, and try to spot where one crew's stretch ends and the next begins.