A conclave is the supremely suspenseful event at which cardinals, also known as princes of the Church, congregate to elect their new leader with help from the Holy Spirit. Conclaves are even more unpredictable than general elections or referendums: according to an old Roman saying, if you go into a conclave as pope, you will leave it as a cardinal. The most favoured candidate is unlikely to be elected. When the white smoke finally rises, it usually turns out that all the bookmakers have got it wrong.

Mary Hollingsworth recounts the events of the Roman conclave of 1559, tracking and tracing the ‘ill-tempered power struggle between the various factions’. In this conclave, three equal factions in the College of Cardinals vied for dominance: the cardinals loyal to the Spanish king; the cardinals loyal to the French crown; and a group of recently created cardinals who had previously owed their allegiance to the deceased pope, Paul IV, and were now led by his nephew. In the first sixty-eight voting rounds, none of the factions became strong enough for their candidates to achieve the required two-thirds majority. And so, Cardinal Ippolito d’Este, the preferred candidate of the French king, never got close to being elected, despite his abundant wealth, charm and tactical manoeuvrings.

The conclave culminated in a surprising outcome. Giovanni Angelo Medici, a compromise candidate who had been on few people’s radar (but was supported by the Medici duke of Florence), was suddenly elected late on Christmas Day and took the name Pius IV. The 1559 conclave was also surprisingly