What two books did Jefferson encode on his cypher? The Koran and DON QUIXOTE.
To understand this, we need to understand something of the history of DON QUIXOTE and its author. Meguel de Cervantes was a Spanish soldier who had fought in numerous battles against the Muslims, including the Battle of Lepanto. This battle proved a decisive victory for European Christians against invading Muslim forces. Though he was weak with fever, Cervantes refused to stay belowdecks and kept fighting, earning him two gunshot wounds to the chest. One wound rendered his left hand and part of his left arm useless for the rest of his life.
Following six months of recuperation, Cervantes rejoined his unit in Naples and remained with them until 1575, when he set sail for Spain. His ship was attaced by the Islamist pirates who murdered the captain and most of the crew. Cervantes and a handful of passengers were taken to Algiers as slaves.