The Medici family bank was founded even before the Banco di San Giorgio, in 1397, and it collapsed in 1494. But the family's lasting creation may be the myth of itself. The Medici were not just brilliant, wealthy, ruthless and powerful; they were a seriously dysfunctional family. This may explain why they offer such rich material for historians and novelists. (See especially April Blood, an account by the historian Lauro Martines of the plot, led by the Pazzi family but involving many others, including the king of Naples and Pope Sixtus IV, to wipe out the Medici family in 1478.)

The Banco di San Giorgio was not a family. It was an institution, bound by secrecy and rules, without any dominant personality. The men who ran it for almost its entire history were public figures, yet little is known of their lives. The bank is the hero of its own story. What is known is that in a short space of time, it became so entwined with the republic of Genoa that the bank and the state were indistinguishable. Machiavelli described the relationship as “a state within a state”. The Banco di San Giorgio grew so influential that it replaced the Fuggers, the German banking dynasty, as the source of financing for Europe's cash-starved, perpetually warring monarchs. A century and a half after it was created it had restored Genoese power and influence as a maritime and commercial state to such an extent that the period from 1557 to 1627 was termed the Age of Genoa by Fernand Braudel, the great French historian (Felloni was his student).

The bank was able to do this because the circumstances in which it operated were particular to Genoa. It was not the personalities who ran the Banco di San Giorgio who were dysfunctional, but the state that had called it into being. Genoa in the 1400s was a peculiar place. Although it was a republic, it was run by aristocrats, and not well, and institutionally it was weaker than Venice or Florence. The Banco di San Giorgio gradually ended this state of affairs, through a creeping takeover of the republic. This is what Machiavelli meant. It is, scholars say, why the history books tend to look askance at the bank: its corporatist modus operandi tends to cloud everything else. “History would tell us that here is a set of bankers who bled the state to death,” observes Michele Fratianni, a professor at the Kelley School of Business at Indiana University who has written extensively about the history of Italian finance.