carry coals to Newcastle

To do something redundant, frivolous, or unnecessary. Newcastle was once a major coal supplier. We definitely don't need to bring any toys when we go over their house—they have so many that bringing more would be like carrying coals to Newcastle. I thought a bottle of wine would be a nice gift, but when I saw their liquor cabinet I could tell that I had carried coals to Newcastle.

Prov. to do something unnecessary; to do something that is redundant or duplicative. (Newcastle is an English town from which coal was shipped to other parts of England.) Mr. Smith is so rich he doesn't need any more money. To give him a gift certificate is like carrying coals to Newcastle.

Do or bring something superfluous or unnecessary, as in Running the sprinkler while it's raining, that's carrying coals to Newcastle. This metaphor was already well known in the mid-1500s, when Newcastle-upon-Tyne had been a major coal-mining center for 400 years. It is heard less often today but is not yet obsolete.

To do something that is unnecessary or superfluous. The Newcastle referred to is the city of Newcastle-upon-Tyne, a seaport in northeastern England that was given a charter to mine coal by Henry III in 1239 and became a major coal center. By the seventeenth century this metaphor for bringing an unneeded thing was current, and it remained so in all English-speaking countries. There were (and are) equivalents in numerous languages. In French it is to carry water to a river.