“MAKING MARKETS SAFE is one of the oldest problems of market design, going back to well before the invention of agriculture, when hunters traded the ax heads and arrowheads that archaeologists today find thousands of miles from where they were made. More recently, one of the responsibilities of kings in medieval Europe was to provide safe passage to and from markets and fairs. For healthy commerce, buyers and sellers needed to be able to participate in these markets safely, without being waylaid and robbed (or worse) by highwaymen. Indeed, the word waylay captures the act of robbing travelers carrying money or valuables on their way to or from a market. Without some assurance of safe passage, these markets would have failed; they would have been too risky to attract many participants. And if the markets had failed, the kingdoms would have been deprived of the prosperity that markets, and the taxes on them, bring.”