Most historians credit the city-state of Florence as the place that started and developed the Italian Renaissance, a process carried out through the patronage and commission of artists during the late 12th century. If Florence has received its due credit, much of it belongs to the House of Medici, the family dynasty of Florence that ruled at the height of the Renaissance. The dynasty held such influence that some of its family members even became pope, and it all started with a banker colloquially known as Cosimo the Elder.

Cosimo’s trajectory was nothing short of incredible. In the spring of 1433, he sat in a small stone cell high in the tower of the Palazzo della Signoria, listening to the bells of the city he had spent his life serving and waiting to learn whether he was to be beheaded. He was 43 and held no public title of consequence, commanded no army, and had taken pains for most of his life to appear as one prosperous citizen among many. Nonetheless, the men who then governed Florence had decided that he was too dangerous to leave at liberty, and for several days the question before the city was not whether Cosimo possessed power but whether the republic dared to kill him for it.

Instead of being executed, within 18 months, he returned from exile to a city that received him as a deliverer, and for the 30 years that followed, he ruled Florence more completely than any king ruled a kingdom, despite never assuming a crown, a permanent office, or a public claim to authority. He governed through a network of friendships, debts, favors, and quiet arrangements so subtly that foreign observers struggled to describe it, but what they saw was plain enough even when the mechanisms by which Cosimo maintained control were not. The peace and the wars of Italy answered to his judgment, and the powerful leaders across the peninsula carried their business to his house, settling across a banker’s table the questions other cities settled in council chambers and throne rooms.