A Rift Key was used by 17-year-old Leonardo da Vinci to return home circa 1469 after being deposited by a rift storm to Torchwood Three's Hub in 1967. Leonardo managed to disable the self-destruct mechanism and drew the inner workings of the Rift Key. The only copy of this drawing was stored in Torchwood. Leonardo helped the Torchwood team with the mathematical equation necessary to send him back. He worked it out in his head. (PROSE: Cultural Firsts)