At the end of summer the Celts
thought the barrier between our world and the world of ghosts and spirits got really thin.
This meant weird creatures with strange powers could wander about on Earth.
The Celts had a big party. It was all about scaring away the ghosts and spirits.
All Hallow's Eve
Later the Christian religion took over. The party stayed on the same day but it was now called All Hallows Eve.
It was the day before All Saints' Day.