For centuries, gold's beauty and relative rarity have made it a recognized medium exchange around the world. Up until recent centuries, almost every currency on the world was on "the gold standard." That is, paper money was understood to be fixed to a specified amount of gold stored in a bank's vaults. It was a much more stable form of currency than the fiat currency nearly all governments issue today.
In the event of a currency collapse, investors around the world expect gold to again be the go-to for trade. In the meantime, it remains an excellent long-term hard investment. Over the course of ten or twenty years its value consistently rises, making it a safer bet than stocks.