The Tomb of Hadrian, or Castle of St. Angelo, as it has been called since the famous vision of Gregory the Great, is a familiar object to every stranger in Rome. It stands above the yellow Tiber facing the ancient Aelian Bridge, now called also the Bridge of St. Angelo on the main road to St. Peter's and the Vatican. It is connected with the latter by a subterranean passage built by Pope Alexander VI in 1500, and used by his successors as a path of retreat to the fortress in times of internal revolt or foreign attack. The great fortress prison, although dismantled of the marble that once covered its stones, is still a most imposing edifice and is second to none in the world in its historic memories, replete with strange and terrible interest. It is an epitome of Roman history, closely associated from the beginning of the Christian era down to the fall of the temporal power of the Popes, with the storms and struggles that have rent the Eternal City. Any account of Italian prisons must thus centre about this grim old relic of the Cæsars,
