Coals to Newcastle

Coals to Newcastle is an old saying that means to do something that isn't necessary. It's used to describe doing something that someone else has already done, or that isn't needed. It comes from a town in England called Newcastle that was famous for coal mining.

Imagine if someone carried a pile of coal to the town of Newcastle. It wouldn't make any sense because the town already has lots of coal, so bringing more there is unnecessary. That's what we mean when we say "carrying coals to Newcastle", it's unnecessary and doesn't make sense!