On one side of the barrier they shouted about the injustices of global capitalism; on the other they sipped beer and snapped pictures of luxury sports cars.
A group of activists, protesting capitalism in general and Quebec's tuition hikes in particular, have been trying their hardest to crash the party on the Montreal street most closely associated with this weekend's Canadian Grand Prix festivities.
There have been some surreal scenes as these two ideological worlds collide.
From the civil conversations to the brief fistfight, the last two nights have written a memorable chapter in the history of Crescent Street, the most notorious party strip in a town that loves its parties.
Crescent has long been a spiritual home to the city's old-time scenesters, the silk-shirted dance divas looking to see and be seen ever since the days of disco.
This weekend it is the epicentre of another phenomenon: Quebec's ongoing ideological struggle.
Protesters haven't gotten as close as they'd like.
While thousands of Formula One fans flocked to Crescent as they do each year for the expensive cars, free swag and popular nightclubs, the demonstrators were kept at bay by lines of riot police.
As the marchers massed on the outside looking in, the party people inside cranked up the dance music to eardrum-rattling decibel levels to drown out their chants Friday night.
Some protesters danced on the edge of the police perimeter as a Lady Gaga lullaby shook the night. One got into an exchange of fisticuffs with a burly pedestrian who tried to take their picture. One was arrested for trying to run around the police line.
The police lines also left some frustrated tourists stranded on the edges of the F1 street party, waiting to get in. Instead, they witnessed things like riot police pepper-spraying and arresting people, as some protesters tossed bottles and other projectiles.
It was a similar scene the previous night.
A protest march that began near a community center in one of the city's working-class neighbourhoods marched its way to Crescent on Thursday, chanting an ethos not commonly associated with the land of two-for-one shooters and heavy cologne.
Sunday's Formula One Grand Prix race, and the events leading up to it, traditionally mark the beginning of Montreal's festival season. The well-heeled Grand Prix crowd can bring in as much as $100 million for the local economy.
It comes at a vital time this year for the city's merchants, who blame the student conflict for lower-than-average sales.
But the importance accorded the race by public officials, especially the Quebec government, has made it a target for the student movement and its supporters.
With negotiations stalled and nightly demonstrations dwindling in size, they have turned the Grand Prix into a fault line in their battle.
They see the conspicuous consumption and flashy cars associated with the event as an insult against their ideals of a more egalitarian society, one characterized by cheap university tuition.
-With files from Peter Rakobowchuk