And what of the Grail, that mysterious object that all the knights-errant were ultimately seeking? Oddly enough, Richard Wagner, composer of the opera Parzifal, first suggested that the Grail was a symbol inspired by the new forms of finance. While earlier epic heroes sought after, and fought over, piles of real, concrete gold and silver—the Nibelung's hoard—these new ones, born of the new commercial economy, pursued purely abstract forms of value. No one, after all, knew precisely what the Grail was… Marc Shell even suggested that it would best be conceived as a blank check, the ultimate financial abstraction.

—David Graeber, Debt: The First 5,000 Years