Manchester derived its name from Mamucium, the Roman name for the 1st century-settlement and fort. Mamucium itself is a Latinised form of the Celtic meaning "breast-shaped hill".
The Latin name for Manchester is often given as Mancunium. This is most likely a retronym coined in Victorian times, similar to the widespread Latin name Cantabrigia for Cambridge (whose actual name in Roman times was Duroliponte. (Wikipedia)
Barcelona is said to have been named for Carthaginian general Hamlicar Barca, who is supposed to have founded it in the 3rd century B.C.