Ship's logs and maps of exploratory voyages were highly prized in the fifteenth and sixteenth centuries, and very secret. They were the key to trade and treasure. The penalty for revealing such information to foreigners was often death. In 1502 the Duke of Ferrara instructed his agent, Alberto Cantino, to acquire information on the latest Portuguese discoveries. Cantino paid twelve gold ducats for a copy of the official Portuguese padron, the world map on which all new discoveries were recorded. It is called Carta de navigar per le Isole nouam tr[ovate] in le parte de India: dono Alberto Cantino al S. Duca Hercole (Chart of the islands recently discovered in the regions of the Indies presented to Ercole d'Este, by Alberto Cantino). The two horizontal red lines are the Tropics of Capricorn and Cancer. The black line between them is the equator. The vertical line labled in red is the Treaty of Tordesillas' line.