London
The name of London is derived from a word Londinium, a latin word. By the first century CE, this was a commercial centre in Roman Britain. The etymology of the name is uncertain.
A couple of researches about King Lud in the City of London led me to this possible explanation of the name.
Lud's name was claimed by Geoffrey of Monmouth to be the origin of Ludgate (named Porth Llydd in the Brut y Brenhinedd), a major gateway into the City of London, as well as of the name of London itself (the true etymology of Ludgate is, however, from the Old English term "hlid-geat" a common Old English compound meaning "postern" or "swing gate".
Geoffrey of Monmouth explained the name "London" as deriving from "Caer Lud", or Lud's Fortress. When he died, he was buried at Ludgate. "Lud's fortress" or a further etymologic interpretation of the name would be "Swing gate's fortress.