Walk past the Palazzaccio, the Palace of Justice, in Rome today and looking down on you is the statue of a man who is unlikely to be immediately recognisable, Bartolus of Saxoferrato. He is extravagantly robed in a faintly comic strutting pose, one hand flamboyantly resting on his hip.

This performative stance is unlikely to have corresponded to his bookish character but perhaps foreshadowed his numerous posthumous theatrical incarnations, including appearances in The Barber of Seville, and The Marriage of Figaro, in which the lawyer figure bears his name. Even long after his death, the name Bartolus was synonymous with the law. As the popular late medieval adage went: nemo bonus íurista nisi bartolista (no one is a good jurist unless he is a follower of Bartolus).

Further statutes in Spain and Portugal, erected in 1427, 1433 and 1446, demonstrate an adulation that is rarely lavished upon the legal class. In the case of Bartolus, however, his opinions were quite literally law. Dissent was unwise. In 1431, the humanist Lorenzo Valla was driven out of the University of Pavia merely for critiquing Bartolus’ antiquated style.

Dry, pious, and obsessive commentaries on Roman law are not the most obvious path to celebrity, especially considering that his interpretations rarely strayed far from the orthodoxies of the day. Perhaps this is why Bartolus’ glittering legal career has been largely forgotten today.

Sometimes, however, the passage of time can reveal as much as it conceals. A closer look at Bartolus from today’s perspective reveals something quite unexpected: a unique window showing how ‘modernity’ slowly emerged out of the medieval world. Without realising it himself, this now forgotten fourteenth-century lawyer fathered a concept which our own century holds very dear, that of popular sovereignty.

Bartolus was born in around 1313, in the small town of Saxoferrato, near Ancona in Italy. Like many bright, well-born boys of his era, when considered old enough he was sent to study law. At the age of 14, he was packed off to the University of Perugia, before his evident success as a student earned him a position at the University of Bologna, the oldest and one of the most prestigious in medieval Europe.

We may not know the specifics of Bartolus’ early university life, but other accounts of medieval students offer a picture of what he might have got up to. Then as now, the idea of university was to train young minds and encourage social mobility by offering a path to power and influence to young men like Bartolus, who were not members of the landed nobility or aristocratic clergy.

The Italian universities, unlike their northern counterparts in Oxford, Cambridge and Paris, were mainly vocational rather than theological, and offered particularly renowned courses in medicine and law. In this sense, they were far more the direct ancestors of the contemporary western university.

For Bartolus and countless young men like him, university offered his first chance to leave home, to visit a city and to try his hand at lifestyles not possible in the more conservative countryside. Though medieval university rules outlawed gambling, overnight visitors and staying out late, contemporary chronicles are filled with disapproving accounts of students fighting and rioting, and ‘town and gown’ clashes with the locals, often over women. Drinking was a heavy part of student culture, as it was across medieval life in the absence of clean water; consuming three or four pints of beer a day was typical from childhood onwards.

At Bologna, Bartolus studied under the most famous jurists of his day and graduated as a Doctor of Medicine (the equivalent of a modern PhD), aged just 21 in 1334. By his mid-twenties, he was teaching at the University of Pisa. Anyone familiar with the world of academia today will be unsurprised to learn that his success attracted professional jealousy. One story, spread by a certain Diplovataccius, has it that he was banished from Pisa for four years for unjustly sentencing a defendant to death. Given the complete dearth of evidence to the claim, it was most likely malign rumour designed to discredit him.

By the time he returned to Perugia in 1343, he was famous across the world of Christian academia, assisted by an astonishing work ethic and a lucrative niche as a legal consultant. We have evidence of almost 400 legal opinions that Bartolus wrote at the request of judges or private parties seeking legal advice, as well as a host of original tracts and detailed commentaries on the entirety of the Roman legal canon. In 1355, the Holy Roman Emperor, Charles IV, appointed him as his own personal legal adviser, an honour marking the zenith of any academic’s career. Bartolus died just two years later, aged 44.

He had been the ultimate advert for the medieval university system, born in rural obscurity but ending his life enjoying the confidence and patronage of God’s ordained ruler. The emperor had ennobled him and conferred various marks of imperial favour, including the concession that Bartolus and all his descendants, should they take up the legal profession, could legitimise future bastard children. This was a major power in a time when bastardy was largely believed to promise damnation.

By Bartolus’ time, the Roman Empire in the west had not existed as a political force for more than 800 years and unity had given way to disharmony as a tide of warring states squabbled over the Roman legacy. Yet educated thinkers such as Bartolus were unwilling to accept that the Empire was completely over or that Christian and legal theory should be entirely reinterpreted. Rather, they believed that the old empire’s universal authority had simply been translated into a new, divinely sanctioned contemporary form — what we now call the Holy Roman Empire — with Pope Leo III crowning Charlemagne emperor in 800. This arcane process was known by scholars as the translatio imperii.

This new God-ordained empire (made most famous by Voltaire’s much later claim that it was neither holy, nor roman, nor an empire) held at least nominal sway over most of central Europe, from the Danish marches in the north to central Italy in the south. It was a regime that remained a potent force and was acutely aware of its own imperial legacy.

By claiming to be descendants of the Caesars, these medieval emperors were also empowered by the famous law code of the sixth century Emperor Justinian, known as the Corpus Juris Civilis. This ‘Roman Law’ was unequivocal when it came to imperial power: ‘all right and all power of the Roman people has been transferred to the imperial power’ and ‘what has pleased the prince has the force of law’.

Whenever imperial authority was challenged, the emperors could justify their actions not only with their divine mandate to rule but by citing this immutable Roman law. The formidable Emperor Barbarossa faced down his enemies at the Diet of Roncaglia in 1158, for instance, by citing the Corpus to confirm that he alone was invested with power. And that was the end of it.

Nonetheless, a highly intelligent man such as Bartolus could not ignore the problems that administering this rigid code presented in an era of overlapping, ill-defined jurisdictions and competing customs. Under the ancient empire, laws had been issued from a clear centre; no other sources of authority or sovereignty had been permitted to exist. Now kaleidoscopic shifts of power over the last millennium had, in reality, created a world where thousands of local or customary laws competed with each other and often directly contradicted the commands of the Corpus. In Italy alone there were hundreds of sources of authority below the level of the emperor. Even cities — such as the highly prosperous and successful Padua and Sienna in northern Italy — had settled into habits of self-governance and did not obey imperial commands.

This tension between local and central government had exercised scholars from the advent of legal studies at Bologna in 1088. Before Bartolus an entire school of lawyers, known as the ‘glossators’ because they devoted their lives to writing glosses, or commentaries on the margins of the Corpus, had tried, unsuccessfully, to solve the problem of adapting the Corpus to the real world in all its variety. They apparently could not conceive of looking beyond the Corpus itself for a solution and so were caught in an intractable merry-go-round of constant trial and error. They did, however, touch, almost by accident, upon one idea that would help to shape Bartolus’ revolutionary thinking. Azo, one of the greatest glossators, argued that custom originating from before the first Roman emperor came to power might still be valid. In other words, he argued, the emperor might rule over every individual person in the Empire, but not the ‘corporation’ of the people who had originally given him his power. What Azo failed to see, or perhaps acknowledge, was where this line of thinking inevitably led: power ultimately came from the people and not the emperor.

It took time for the idea to percolate through. Bartolus inhabited the same intellectual world as Azo, making the traditional half-baked attempts to defend the universal monarchy’s relevance, such as an old argument that distinct territories with their own laws were actually just like the provinces of the classical Roman Empire. However, there was one, crucially important difference between Bartolus and Azo. Bartolus was willing to at least discuss the legitimacy of de facto independent city-states that existed in northern and central Italy, without immediately discounting anything not determined by the Corpus.

Rather than dismissing it as a subject unworthy of comment, Bartolus argued that if a city can demonstrate the power to appoint officials and make its own laws, then that power must exist, even if the Corpus decreed otherwise. Where Azo would have seen a logical problem to overcome, Bartolus deemed this state of affairs a reality worthy of analysis. This ability to make empirical judgements set Bartolus apart from all those who came before him and heralded the end of medieval conceptions of authority.

Bartolus also drew on Azo’s idea that sovereignty rested in the ‘corporation’ of the people. Where Azo had seen this in terms of a specific and irrevocable historical event, Bartolus used the idea to explain the autonomy of the ‘free cities’. He argued that if it was provable that the people could govern a city independently and effectively, then the city must answer only to itself. He called this concept civitas sibi princeps — the citizen body is its own superior. The European Union today calls it subsidiarity.

If people make up a political body, then the existence of that body is not dependent on whichever regime is currently in charge. The people define themselves from a sense of shared identity and custom. Not only does this idea go some way towards explaining people’s right to independence from empires, but it also points towards a remarkably modern idea of sovereignty as a citizen body that makes its own laws and appoints its own officials.

Bartolus was, of course, still a man of his time. His argument is still framed by the language of usurpation, and therefore falls in on itself. ‘A city can prove itself not to be a usurper if it has been a usurper for long enough.’ He would never have contemplated abandoning the structure of the empire (not least because he would have been out of a job) and would have been horrified by the implications of his own argument — that de facto independence could justify real independence and flout the laws of the Corpus. In attempting to explain the existence of a phenomenon that he disapproved of, this staunch imperialist had stumbled across an idea that would later lead to the death of empires and sow the seeds of nationalist and resistance movements through the centuries.

We know less about Bartolus the man than we do about Bartolus the lawyer and most of what we do know is from his will. His life was far from that of a revolutionary. While he may have had the power to un-bastardise children, it seems his own at least were born in wedlock. He was married twice, and though little information survives about his first wife, we can name his second — Pellina di Bovarello of Perugia, who survived him and was the mother of his two sons and four daughters. His will designated his two sons as his principal heirs, but he did not completely overlook the women in his family. He left his daughters 450 florins each and made a suitable provision for his wife. He was interred under a monument bearing the pleasingly simple inscription, Ossa Bartoli, ‘the bones of Bartolus’.