Halloween is the night before the All Saints Day. The Old Celts celebrated November 1 as the beginning of a new year and the celebration was dedicated to the god of Sun, but also to the master of death, Samhain.
They believed that during the full moon, the night before the day of the dead, the dead leave their graves and visit their homes. That is why the living ones disguised themselves and made noise.
Pumpkins didn’t become popular until 16th century, and carving pumpkins was first popularized in America and then throughout the world.