E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Newcastle (Northumberland)
was once called Moncaster, from the monks who settled there in Anglo-Saxon times; it was called Newcastle from the castle built there by Robert, son of the Conqueror, in 1080, to defend the neighbourhood from the Scots.
1
Newcastle (Staffordshire) is so called from the new castle built to supply the place of an older one which stood at Chesterton-under-Line, about two miles distant.
2
Carry coals to Newcastle. A work of supererogation, Newcastle being the great seat of coals. The Latins have Aquam mari infundre (To pour water into the sea); Sidera clo addre (To add stars to the sky); Noctas Athénas (To carry owls to Athens, which abounds in them).