Walk past almost any old farmhouse in Ireland or the west of England and you will see one: a rusty iron horseshoe nailed above the door.

The tradition goes back well over a thousand years.

Iron was expensive and rare — a full set of shoes was a small fortune to a medieval farmer — and folk stories said that iron itself frightened away mischief.

Which way up should it hang?

Every village argues.

Some say points-up, so the luck stays cupped inside; some say points-down, so the luck pours out onto whoever walks under it.

The oldest surviving guides, written in the 1500s, prefer points-up.

Blacksmiths, who worked with the iron and the fire, were treated as almost-magicians in their own right — the last blacksmith of Gretna Green in Scotland was still marrying runaway couples over his anvil in the 1940s.

Try this: next time you see a horseshoe on a door, notice which way it points, and ask who put it there.