They also seemed "well trained," Marseille prosecutor Brice Robin observed, carrying out what seemed like planned attacks on rival fans with military precision.
Europe, it seems, has just encountered the Russian ultras: fanatical football hooligan "firms," linked with various Russian teams, bent on racism and violence.
Via social media, CNN made contact with one ultra who says he took part in the rampage through Marseille, after the game with England early in the Euro 2016 championship.
He spoke on condition of anonymity, but described why the violence took place.
"I was one of the people who drove the English fans through the city's streets
," he told us via his social networking page.
"There are not so many of us as the English, therefore we just gathered in one place and moved towards the port. The English fans consistently provoked some of our compatriots but avoided direct contact -- they threw whatever they had to hand (stones, bottles, chairs) and then ran away like cowards. So it's time to punish them for their behavior," he added.
Expelled from Marseille
The prefect in the French region of Provence, which includes Marseille, signed expulsion orders Thursday for 20 Russian citizens after violence around the Euro 2016 match between England and Russia last Saturday.
The 20 -- between the ages of 25 and 40 -- were arrested after allegedly taking part in clashes between fans. They are being held at a detention center in Marseille and must leave French territory by Monday.
The Union of Russian Fans said on its website Thursday, "The delegation of the Union of Russian Fans, whose bus was stopped on 14 June on the way from Marseille to Lille, spent more than a day under arrest.
"Twenty people were later released and 20 others, including URF head Alexander Shprygin, were taken to a deportation center from where they will be expelled from France within five days."
Also, the Marseille Prosecutor's Office said three Russian citizens have been sentenced to jail since the clashes last week -- one for a term of two years, another for one year and a third for six months.
Martial arts training
Even the names of the Russian ultra gangs conjure up images of ruthlessness, or warriors going to battle: the Orel Butchers, Torpedo, the Spartak Gladiators.
Some members train as fighters, practicing martial arts and -- unlike their 1980s English hooligan predecessors, on which it's said they model themselves -- emphasize physical fitness over beer-swilling.
There may even be a military aspect to the gangs.
In a recent report, the independent Sova Center
, which monitors racism in Russia, warned that hooligan fans had joined militias fighting on both sides of the war in Eastern Ukraine, returning with potentially dangerous conflict experience.
But perhaps the most worrying aspect of the Russian ultra phenomenon is the level of support, or tolerance, it appears to enjoy at home.
It's hard to imagine officials in, say, Britain condoning the kind of violence witnessed in Marseille. But in Russia, social commentators, even politicians, voiced praise.
One member of the Russian parliament, Igor Lebedev, tweeted that "I see nothing wrong with football fans fighting."
He even urged Russian fans to "keep up the good work."
Lebedev later told CNN he was taken out of context, and that he welcomed the UEFA decision to impose a suspended disqualification on Russia.
The Kremlin condemned the violence and called on Russian fans to behave.
But amid a French crackdown on the hooligans, some of whom were detained on a fan bus en route to Russia's next match, the Russian foreign ministry summoned the French ambassador.
Further "anti-Russian sentiment," as the Russian foreign ministry called it, could harm Moscow-Paris relations.
For a country set to host the biggest football tournament of them all in 2018, they are mixed messages indeed.