There is a panoply of 300-year-old grafitti along the walls of many of the Castillo's casemates. The conscripted soldiers of the mighty Spanish Empire, billions of miles from home and bored out of their minds, found little to do when not on duty once the batteries in their iPhones gave out. Several depictions of ships, which were these soldiers' lifeline to home, and various semi-coherent scribblings are carefully protected and documented with informational plaques. What we're looking at here is likely the work of a soldier who was learning to read and write.