Commentary Inf XXVI 100-111

He and his crew of aging, tired sailors head out across the Mediterranean from Italy and reach the gates of Hercules, the very sign, even as Ulysses reports it, of the end of the known world. While Dante does not refer to it (nor to the previous voyages of Marco Polo), a number of recent commentators speculate that he was aware of the voyage of the Vivaldi brothers in 1291. They, in search of India, sailed out through the Strait of Gibraltar, having passed Spain and Africa, and were never heard from again.