When Giovanni di Bicci de’Medici, founder of the Medici Bank, died in 1429, he advised his children to ‘stay out of the public eye’. Never can paternal advice have been so ignored. Giovanni’s descendants left monuments to themselves all over Florence, and changed the political and financial scene in Italy for ever.

Giovanni registered the Medici Bank in Florence in 1397. Immediately he was told by a fellow merchant, ‘Nobody will ever think of you as an honest trader again.’ In the Divine Comedy, Dante reserves the third ditch of the seventh circle of hell for the usurers, the blasphemers, and the sodomites. Why was it, Tim Parks asks, that usury was not just a sin, but the sin on the minds of wealthy men approaching their deathbeds? He quotes Thomas Aquinas: ‘God creates work to complete man’s nature. Refusing work, the usurer rejects nature, rejects the way God has chosen for him.’

So starting up a bank in Florence at the end of the fourteenth century was not only fraught with implications for your soul, but, as Parks explains, extremely complicated in practical terms. Ships could be lost or attacked at sea, and transferring funds involved sending cash hidden in bales of