Cambium non est mutuum: exchange and interest rates in medieval Europe
利用1383-1411年普拉托商人达蒂尼档案中的汇率数据，研究发现中世纪市场汇率隐含了货币的时间价值，且隐含利率与商业贷款利率相当，但汇兑交易存在不确定性，可能使其免于高利贷指控。
A major gap in our understanding of the medieval economy concerns interest rates, especially relating to commercial credit. Although direct evidence about interest rates is scattered and anecdotal, there is much more surviving information about exchange rates. Since both contemporaries and historians have suggested that exchange and rechange transactions could be used to disguise the charging of interest in order to circumvent the usury prohibition, it should be possible to back out implied interest rates from exchange rates. The analysis presented in this article is based on a new dataset of medieval exchange rates collected from commercial correspondence in the archive of Francesco di Marco Datini of Prato, c . 1383–1411. It demonstrates that the time value of money was consistently incorporated into market exchange rates. Moreover, these implicit interest rates are broadly comparable to those received from other types of commercial loan and investment. Although on average profitable, the return on any individual exchange and rechange transaction did involve a degree of uncertainty that may have justified their non‐usurious nature. However, there were also practical reasons why medieval merchants may have used foreign exchange transactions as a means of extending credit.