David Cameron said last year he had "serious concerns" about crossing it. Mick Jagger sang with anguish on Streets of Love that he thought he might have done so. One man who definitely did make his way over the Rubicon, triggering civil war in ancient Rome and ensuring the river's place in common parlance for the millennia to come, was Julius Caesar.

But if anyone tried to follow in his footsteps now, they might have some difficulty. According to local historians in north-eastern Italy, the question of which modern waterway lays the greatest claim to being the famous river – or, at least, its closest descendant – is anything but settled.

On Saturday, in the usually peaceful town of San Mauro Pascoli, near Rimini, the centuries-old debate will be reopened in a mock trial that aims to deliver a verdict, once and for all, on the identity of the real Rubicon. It is a battle that pitches neighbouring towns against each other and divides impassioned locals into three equally zealous camps – one for each river in question.

Fierce as Caesar's battle with Pompey was, it may have nothing on this. The judge, however, is expected to draw the line at severed heads.

In 1933, a time when Benito Mussolini was fully versed in the rehabilitation of Rome's ancient glory for contemporary political purposes, he decided the debate over the Rubicon had gone on long enough. The fascist dictator renamed the little Fiumicino river in his native Emilia Romagna the Rubicone, and decreed that the town through which it ran should also henceforth be known as Savignano sul Rubicone.

But the official ruling did nothing to deter those who believed that their river – either the Uso or the Pisciatello – was the genuine article. "There was no definitive proof. The debate, which had been going on for centuries, was still open," said Paolo Turroni, a teacher and journalist from Cesena who will present the case for the Pisciatello on Saturday. "In reality, Mussolini had political reasons for doing what he did. At that time the podestà [mayor] of Savignano was an important figure in the Fascist party."

Rubicon locator.

Over time, however, the Fiumicino's credentials have convinced many that it is indeed the right choice. Giancarlo Mazzuca, a newspaper editor, writer and former MP for Silvio Berlusconi's centre-right People of Freedom party, will argue at the mock trial that the Fiumicino deserves to keep its title due, among other things, to the Tabula Peutingeriana, a medieval copy of a Roman road map, which places the Rubicon 12 miles from Rimini on the Via Aemilia. The river also, he notes, has a bridge built in Roman times.

"This history is often overlooked due to the fact that the person who gave this order was Benito Mussolini. On the other hand, the foreign press, including the Times of London, had already said in 1932 … that the real Rubicon of Julius Caesar is indeed that of Savignano," he wrote in notes for the Sammauroindustria cultural association, which is organising the event.

For others, though, this is a historical injustice. Turroni says he will use various pieces of evidence including Vatican maps, ancient parchments and even Giovanni Boccaccio, author of The Decameron, to prove beyond reasonable doubt that the Pisciatello is the closest thing to the ancient Rubicon as is possible given the huge territorial changes that have taken place since 49BC. He and his fellow believers say they have evidence identifying their river as the Rubicon dating as far back as the 10th century, and claim that its colloquial name – the Urgòn – could easily have evolved from Rubicon.

Meanwhile, archaeologist Cristina Ravara Montebelli will fight the case for the Uso, which she says has long been regarded by historians and writers from Rimini as the original river. Her argument will hinge, among other points, on the existence of Roman-era ruins in the area. Even in 1750, she says, the spot had come to be considered by some to mark the ancient border with Cisalpine Gaul – in other words, the Rubicon.

The mock trial on Saturday will not be the first set up by the Sammauroindustria, whose president, Gianfranco Miro Gori, came up with the idea as a means of exploring history in an inventive and exciting way. Past years have put on trial issues surrounding characters such as unification hero Giuseppe Garibaldi and Mussolini himself. "The Rubicon is very local in one way, but has international dimensions," he said.

Turroni said the Rubicon issue had regained its prominence over the past 20 years. Locals, he added, were proud of their river's origins. But, despite the rivalry, "it's always in good cheer and never anger," he added.