Many visitors to Venice will spend an evening on the Fondamenta della Misericordia, in the northernmost sestiere of Cannaregio, one of the city’s liveliest wine and cicchetti hotspots. But take just a short walk to the Bridge of Santa Fosca and the canals grow quieter. Suddenly it is easier to imagine Venice as it was on the night of 5 October 1607, when the bridge became the site of an attempted political assassination that shook Europe.

The would-be victim was Paolo Sarpi, a Servite friar and state theologian to the Serene Republic of Venice. The assassins were suspected papal agents. After he was stabbed, Sarpi – whose sangfroid became part of his legend – quipped that he recognised the stilum Romanae Curiae (the style, or stiletto, of the Roman Curia). Portraits painted of him after the incident feature a black patch, hiding his wounds. Today, the event is marked by a bronze statue of Sarpi, erected in 1892, a few steps away from both the site of the attack and Sarpi’s long-term home in the Servite monastery. Back at the time of Sarpi’s death in 1623, a proposed memorial had to be abandoned to avoid a diplomatic rift with Rome.

Sarpi’s notoriety stemmed from his prominent role in the Venetian Interdict controversy (1606-7), one of the major international crises of the early seventeenth century. In April 1606, following a dispute over Venetian laws governing Church property, Pope Paul V placed Venice under Interdict, banning religious services across Venetian territory. A largely unfamiliar concept today, proclaiming an interdict was the papacy’s strongest weapon, aiming to bring everyday spiritual life to a standstill: no baptisms, no marriages, no burials. In the months that followed, Venetian writers – Sarpi most prominent among them – defended the Republic’s stance in a series of pamphlets, galvanising opinion across Europe.

On the Roman side, the theologian Cardinal Robert Bellarmine argued that the Pope possessed an ‘indirect’ right to intervene in secular affairs if a ruler endangered souls by acting contrary to religion. For Bellarmine, this was exactly what had happened: Venice had sinned by impinging on ecclesiastical rights. But Sarpi saw things differently, fearing that Bellarmine’s arguments paved the way for a universal papal monarchy and the total extinction of princely power. If the Pope exercised jurisdiction over all matters of sin – and, crucially, was the judge of what constituted a sin – then the Pope could claim secular power whenever he liked, in Venice or elsewhere. The laws and independence of all states were at risk; thus the Venetian cause became, in the words of one of Sarpi’s admirers, ‘the cause of all princes in common’.

The Interdict debate occurred at a moment of transition in the theory of international relations. For Sarpi, the world was divided into multiple independent states, ruled by different absolute sovereigns. There is no room in this account for the supranational papal claims advocated by Bellarmine, which operated across national divides. Rejecting the pre-Reformation reliance on the overarching authority of the pope or Holy Roman Emperor, Sarpi embraced a vision of discrete states that looked a lot like ‘Westphalian sovereignty’, long before 1648. His pamphlets make clear that ideals of unitary sovereignty did not emerge fully formed with Thomas Hobbes or the Peace of Westphalia: they were a product of decades of contested claims about papal power.

Coming just months after the discovery of the Catholic Gunpowder Plot on 5 November 1605, Sarpi’s writings had particular resonance in England. The English Ambassador to Venice, Sir Henry Wotton, and his chaplain, William Bedell, saw an opportunity to encourage a permanent Venetian break with Rome. They cultivated links with the Venetian anti-papal party and coordinated the translation and publication of various pamphlets, including Sarpi’s, in London. Sarpi began regular clandestine meetings with Protestants, which continued even after the Interdict was lifted in April 1607. Bedell made weekly visits to the Servite monastery (just five minutes up the canal from the English ambassador’s house) on the pretext of teaching the friars English. Other political socialising took place in shops, barbers and pharmacies. As all present could claim independent reasons to be there, difficult questions could be avoided.

Sarpi’s great fear was a universal papal monarchy, underpinned by the intellectual claims of Rome and the military might of pro-papal Spain. To avoid this fate, he sought an anti-papal and anti-Spanish league between Venice and other sympathetic states. The first two decades of the seventeenth-century were a time of relative peace in Europe, in contrast to the destructive religious wars of the late 1500s. But observers knew that existing peace settlements were fragile. The defenestration of Prague (1618) was just one incident in the new wave of confessional violence that marked the first phase of the Thirty Years War. Sarpi spent his life trying to ensure that such a war would not result in Hispano-Papal hegemony.

Sarpi’s cloak-and-dagger Venetian world had many of the hallmarks of a Cold War thriller: stark ideological division, covert meetings, lurking double agents, political assassination, and the looming threat of a catastrophic all-out war. For his Protestant interlocutors, Sarpi took on a role akin to that of Vaclav Havel and Soviet dissidents of the late twentieth century, bravely attempting to ‘live within the truth’, in a Church and state marred by Romish corruption. For Sarpi himself, however, his position was more ambiguous, requiring chameleonic dissimulation at every turn, as he balanced loyalty to Venice with criticism of its ecclesiastical structures. It was, he wrote, impossible to live in Italy without a mask.

Sarpi was also on the frontline of the rapid shifts in scientific thinking taking place in Venice and Padua. In 1609, Sarpi’s account of a poor-quality telescope offered to the Senate for sale prompted his friend Galileo to design a better telescope of his own. Galileo, with eyes on Florentine patronage, later distanced himself from Sarpi and other Venetian contacts: as today, the world of scientific enquiry was not immune to political pressure. It did not do Galileo much good; had he stayed in Venice, he would have enjoyed greater protection (rogue assassins excepted) from papal displeasure.

Sarpi’s surviving papers include scattered private notes (his Pensieri, or ‘thoughts’) exploring the more controversial implications of new scientific and philosophical thinking. Sarpi’s unflinching willingness to unpack unorthodox ideas, especially the possibility of a society of atheists, led the historian David Wootton to label him a moral atheist – perhaps even history’s first. It is hard to make any definitive judgement on Sarpi’s innermost beliefs on the basis of his piecemeal and experimental Pensieri, but his views were certainly shaped by a strong strain of scepticism.

Though the Pensieri were never intended for a public audience, works published in Sarpi’s lifetime also display a deep interest in religion and its social role. Sarpi developed a distinctive interpretation of ‘civil religion’, arguing that Church government should support political stability. He insisted that the Church possessed no coercive powers except those granted by the secular ruler, who could revoke them at will. Sarpi’s subjugation of Church to state made him a hero to later critics of ‘priestcraft’.

The Church of Rome was, for Sarpi, the ultimate example of civil religion gone wrong. He developed a detailed critique of papal overreach, tracing the Pope’s usurpation of secular power as a historical phenomenon. His central thesis was this: if papal power was historically constructed, it could also be deconstructed. This was this goal of Sarpi’s most famous work, his mammoth History of the Council of Trent, published in London in Italian, Latin and English in 1619-20, by James VI and I’s own printer. The manuscript had been smuggled to England in the guise of ‘songs’ (canzoni) sent to the Archbishop of Canterbury, George Abbot.

Sarpi described his History as ‘the Iliad of our age’; clerical usurpations had become a form of warfare, waged on an epic scale. The book was a blistering critique of the Council of Trent (1545-63), the papacy’s attempt at doctrinal retrenchment following the Reformation. Taking inspiration from Tacitus, whose histories exposed the deceptions behind Roman imperial rule, Sarpi aimed to show papal power for the trick it was. Far from being divinely ordained for all time, the rights claimed by Rome were merely the constructions of greedy and ambitious popes. Sarpi became, in Milton’s words, ‘the great unmasker’.

The History was circulated and praised across the Protestant world; Sarpi’s admirers (and imitators) included Gilbert Burnet, Edward Gibbon and Lord Macaulay. His sharp, ironic style retains its appeal today, in both Italian and English. In England, the History proved particularly useful to the Erastian Whigs of the later seventeenth century. Sarpi offered a model for deconstructing the divine-right pretensions of their Catholic and High Church opponents, thus lending authoritative support to the Revolution of 1688, in which the Catholic James II was ousted in favour of his Protestant son-in-law and daughter, William and Mary. In Mary’s funeral sermon, Sarpi’s History was singled out as a book which the late Queen ‘much valued and often took into her hands’.

Alongside defenders of an Erastian Church of England, such as Burnet, Sarpi also inspired more radical critics of episcopacy including John Milton and John Toland. Sarpi almost certainly met – and definitely influenced – the British political philosopher Thomas Hobbes, who travelled to Venice as tutor to Sir William Cavendish in 1614. A long-running correspondence between Cavendish and Sarpi’s close friend, Fulgenzio Micanzio, survives in Hobbes’s own translation. Hobbes shared Sarpi’s horror at papal incursions into the power of secular sovereigns: Bellarmine is the only modern author named and refuted at length in Leviathan. On the book’s famous frontispiece, religious threats to government are depicted in panels on the bottom right. They include a thunderbolt: the fulmen of excommunication and interdict.

For all his seventeenth- and eighteenth-century omnipresence, Sarpi is little known today. His writings, suffused with historical detail and closely tied to their original controversial context, do not easily slot into reading lists as works of timeless abstraction. The Sarpian portions of Leviathan are now the book’s least-read chapters. Yet it was Sarpi’s sharp focus on the specific controversies of his day which made his interventions so powerful. Beyond the world of theory, he was a superlative political operator. He made innovative use of print to shape opinion and recognised the importance of active participation in broader political and intellectual networks. Rather than abstract theorising, he focused his efforts on works with a precise political aim: polemical pamphlets, histories and statements of advice (consulti) addressing specific questions for the Venetian government. For Sarpi, politics was a battle, always shaped by circumstance and contingency, just as the decisions of the Council of Trent had been. By throwing himself into the fray, he did more to shape European political debate than almost any of his contemporaries.