Naples was an Italian city, proximate to the city-state of San Martino.
Guests from Naples were expected at the ball held by Count Giuliano in San Martino that the Fourth Doctor and Sarah Jane Smith attended around 1492. (TV: The Masque of Mandragora)
In 1987, David Gosthorpe died of a stroke while in Naples. (PROSE: Past Reckoning)
Later, it was the intended destination of the Ninth Doctor when he took Rose Tyler for her first trip back in her relative history. (TV: The Unquiet Dead)
Lobus Caecilius, a native of Roman Pompeii in 79 AD, wondered if "San Francisco" referred to a restaurant in Naples upon hearing it mentioned by the Tenth Doctor. (TV: The Fires of Pompeii)
Naples was one of ten major cities across the world, all of which had underground railways, where Coldfire Construction built a reactor within a period of 18 months as part of a plot by the Slitheen to drain the Sun's energy, operated by at least one Slitheen disguised using a skin suit made from a local. At somepoint in 2008, after Sarah Jane Smith foiled the Slitheen with the help of her friends at Park Vale Comprehensive School at Ealing in London, she contacted UNIT so they would clear up the Coldfire sites. (TV: Revenge of the Slitheen)