After the Philistines had captured the Ark of God, they took it from Ebenezer to Ashdod.
They carried it into Dagon's temple and put it next to Dagon.
When the people of Ashdod rose early the next morning, they found that Dagon had fallen on his face on the ground before the Ark of the Lord. So they put Dagon back in his place.
The next morning when they rose, they again found Dagon fallen on the ground before the Ark of the Lord. His head and hands had broken off and were lying in the doorway. Only his body was still in one piece.
So, even today, Dagon's priests and others who enter his temple at Ashdod refuse to step on the doorsill.