When the world still operated on the gold standard, gold bullion was the perfect hedge against inflation. Dollars (and pounds et al) were priced in gold, and so any inflationary measure that devalued the dollar would have a theoretically perfect mirror in the price of gold.

That's obviously no longer the case, but the fact remains that gold is a tangible asset universally recognized as valuable. There are other such assets, but most of them are either commodities with a shelf life (like crops and refined oil), or bulky capital assets (like industrial equipment). And that's discounting the fact that inflation often causes economic decline, lowering the relative value of said marketable assets, even if they are performing relatively better than the currency they are valued in.