Following clashes between Celtic and Rangers fans in Glasgow on Sunday, renewed focus has been placed on the issue of hooliganism and, in particular, the 'ultra' movement.

Scenes of rival groups, their faces covered, tearing through the streets around Christmas shoppers have led some to warn Scottish football is headed back to the dark days of the 1980s.

Where 40 years ago though violence came from 'firms', today's hardcore supporters are known as 'ultras' and while some of the behaviour may be the same, the two are very distinct entities.

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While the exact origin of the movement is hard to quantify, the ultra scene as it's recognised today was established in Italy in the 1950s.

The term comes from the Latin prefix meaning "to go beyond", and signifies the devotion to their club which differentiates the ultras from the ordinary fans.

They're best known for their vociferous support and intricate displays known as a coreografia or, in the UK, a tifo (derived from the Italian word for fan).

The ultra movement is sometimes described as being 'Italy's punk scene', with young men and women throwing off the conservative shackles of the older generation and embracing a more rebellious way of life.

During gli anni di piombo, 'the years of lead', between the end of the 1960s and the beginning of the 1980s, in which hard-left and far-right groups engaged in violence, extremism and even terrorist attacks; the terraces too became politically active with many - but not all - groups taking political stances.

Lazio's Irriducibili and Hellas Verona's Brigate Gialloblu became known for having extreme right and in some cases openly fascist views, while the likes of Livorno and Roma's Fedayn (an Italianisation of the Arabic for 'self-sacrificers') displayed images of Che Guevara and sang 'Bella Ciao' from the stands.

In his book Faccetta Biancoceleste the former Lazio ultra Stefano Greco writes: "In those years for us the stadium was supporting, but also politics and violence. Because politics and violence are part of everyday life - not that it's a justification."

While the terms are often used interchangeably, ultras and hooligans are not the same thing.

The 'firms' which battled on the streets in Britain in the 1970s and 80s were loosely organised, lacking in a clear structure and altogether more spontaneous - and therefore difficult to control for the police.

Ultras are nothing if not organised. Each group - and often there are several within one stand - has its own leaders, members pay dues to fund the colourful displays which greet the teams as they come onto the field, and many even have their own club houses or bars.

Inter ultras display a coreografia (Image: Getty) Unlike in the British hooligan scene there has never been anything to stop a woman being an ultra, and members live by a strict set of rules.

While for hooligan firms any opposition team is the enemy, Italian ultra groups will often form friendships with those from other clubs.

When these are solidified into a formal alliance - a gemellaggio or 'twinning' - matches between the two sides will see one group of ultras singing songs in honour of the other and vice-versa.

The end of a gemellaggio is almost a diplomatic event, with formal notice given and symbolic gestures made.

Genoa and Napoli ultras formed an alliance in 1982 after the former narrowly survived relegation in a 2-2 draw and that remained in place until 2019 when, following a Genoa banner honouring an ultra, Daniele ‘Dede’ Belardinelli, who was killed amid clashes with Neapolitan fans in Milan, the Napoli fans ended it.

"After months of long and deafening silences, a relationship characterized over the years by intense colours, fades into a monochromatic Sunday in April," they said in a statement, perhaps rather melodramatically.

Symbology is important, with the greatest ignominy an ultra group can suffer being the theft of their flag, which would then be displayed upside-down by its captors - honour dictates that a group which has been so shamed should immediately disband.

Crucially, while for hooligan firms violence is the point, for ultra groups it's just one part of the experience. It does happen, and is frequently horrific, but it's not the raison d'être.

For ultras the goal is to make the stadium as noisy and intimidating as possible, with the leaders of the groups barely seeing any of the games as they lead their troops in song through megaphones, their backs to the pitch.

Humour is also an important component. One famous back-and-forth involved Verona fans unveiling a banner against Napoli reading 'welcome to Italy', the implication being that the south is hopelessly backward. The Neapolitan visitors responded with one reading 'Juliet was a whore'.

St Mirren fans visiting Rangers in 2018 got wind of a display which would read 'Our Club. Our City'. When the cards went up they unveiled a banner reading: "Your club is dead, your city is s***e."

From Italy the ultra movement spread to Spain and the Balkans, with Yugoslavia's ultras considered particularly fearsome.

A match between Dinamo Zagreb and Red Star Belgrade in May 1990 descended into a riot which, for some, marked the beginning of the bloody Yugoslav civil war. Zvonimir Boban, the Dinamo playmaker, was snapped booting a police officer who was batonning a Croat fan and was then backed up by the Bad Blue Boys ultras.

Željko Ražnatović, the infamous Serbian warlord known as Arkan, was the leader of Red Star's Delije before the war and it was from the terraces he drew many of his 'Tigers' for the Serb Volunteer Guard which committed some of the worst atrocities of the conflict.

Red Star ultras (Image: Wikimedia) With the fall of communism ultra movements sprang up across central and Eastern Europe, including the Green Monsters of Ferencváros and Legia Warsaw's Teddy Boys, both formed in 1995.

As might be obvious from the names, the ultra movement borrowed heavily from the English hooligan movement - particularly the dress code - in the late 80s and early 90s and so, too, British fans began to ape the ultras.

In the 1990s and early 2000s Italy's Serie A was the best and most glamorous league in the world, attracting the best players as Italian teams dominated European competition.

During that time Channel 4 would broadcast Football Italia to the nation, with the spectacular coreografie beamed into the nation's living rooms. It's no wonder it had an impact.

The Green Brigade formed in 2006 with the Union Bears following a year later, both following the ultra playbook with banners, drums and pyrotechnics.

For better and for worse, they and other Scottish ultra groups are rather a facsimile of what you'll find in Italy, the Balkans or Eastern Europe.

The displays are, broadly speaking, a diet version of some of the more spectacular ones you'd find in Serie A and so, thankfully, are some of the more unsavoury behaviours.

Sunday's scenes in Glasgow may have been unpleasant but there were no reports of serious injuries. On the continent it's uncommon, but hardly unheard of, for there to be deaths.

Many ultra groups in Italy have been infiltrated by organised crime, with mafia groups using tickets allocated to the ultras for their own profit and to launder cash.

In addition, racist chanting is an all-too-common phenomenon among ultra groups, with UEFA and national leagues frequently closing sections of stadiums to punish such behaviour.

While they bring positives in terms of noise, passion and colour there's a darker side to the movement that goes beyond scaring some shoppers.