coals to Newcastle

Etymology
and were major -exporting cities, so sending coal there would be pointless.

Noun

 * 1)  A pointless venture, in the sense of sending something to a place where it is made, or where they already have an abundance.
 * 2) * 1935, attributed to (but possibly a then-circulating joke; see wikiquote):
 * No more coals to Newcastle, no more Hoares to Paris.