Taking coals to Newcastle

Newcastle-upon-Tyne sat at the centre of England's coal-mining and coal-exporting industry from at least the 16th century onward, shipping coal to London and beyond. Bringing coal to a city that already produced and exported enormous quantities of it was the definition of a wasted errand. The phrase is recorded in print from the 1600s and needed no explaining even then, since Newcastle's coal trade was common knowledge across England.