These were used as a cheaper version of a post maul...anywhere that you needed a "big hammer". I remember when the circus would come to town on the train. After a procession down main street, they would start setting up their tent. There was always an elephant that could handle a big wooden mallet to drive the tent stakes.
It looks like yours had iron bands around each end originally to keep it from splitting. They usually became loose and fell off when the wood dried out. Look around, they might still be near where you found the mallet.