Tens of thousands of protesters rallied across Russia June 12. The demonstrations follow March 26 nationwide anti-corruption protests. (Sarah Parnass,David Filipov,Andrew Roth/The Washington Post)

MOSCOW — For years now, history has served as a metaphorical battlefield in Russia, a place where political rivals work to recast the past to justify their struggles to shape Russia's future.

For a few hours on Monday, however, history took the form of a literal battlefield when an enormous Moscow festival resembling a Renaissance fair became the site of clashes between police and anti-corruption protesters.

It may have been the anti-Putin opposition's most surreal protest ever.

Moscow officials had signed off on all manner of spectacles marking Russia Day, a national holiday: carefully reconstructed battles between medieval Russian knights and the Golden Horde; fencers in tights; men dressed in Russian uniforms from both world wars; even folks masquerading as members of the infamous Stalin-era NKVD secret police.

But by late afternoon, the reenactors themselves were under siege. After escorting women in medieval dresses into a tent, a gaggle of knights braced in an impromptu phalanx, their wooden shields forming a wall, as riot police armed with truncheons pushed forward against opposition protesters. Nearby, police swarmed around a replica Viking ship.

Hours earlier, when I first arrived, the protest movement's decision to move its rally to the site of the fair appeared risky. There were families with children, as well as enormous tents and other obstacles that could turn a wave of protesters fleeing police into tragedy if a stampede began.

Then there were the model weapons. In Ukraine, it had taken months of violence before protesters began forging an armory of medieval weaponry to fend off riot police, including homemade clubs, maces and even a do-it-yourself trebuchet.

At the Moscow fair, organized by a reenactment company called Times and Epochs, dozens of (model) melee weapons were in place: halberds and pikes, hammers and wooden shields, fencing foils and tank traps.

Close to the Kremlin, sandbags had been put in place. There was even a station for bayonet practice.

But to the protesters' credit, they never resorted to weapons, even as clashes erupted and police began making arrests. A British colleague told me as we watched students climb the scaffolding of a building overlooking Tverskaya Street, the Muscovite equivalent of Fifth Avenue: "If this were in London, that scaffolding would already be on fire."

Monday's protests may have major repercussions. The Kremlin appeared impervious to criticism next day, shrugging off concerns that police in nearly 200 Russian cities had been too rough on protesters or that protest leader Alexei Navalny — who was later jailed for 30 days — posed a political threat, my colleague David Filipov wrote Tuesday. Years of prison time could eventually be doled out to protesters convicted of attacking police, as happened after a protest March 26.

Meanwhile, sharp-eyed Ukrainian journalists noted that a leader of the Russian riot police appeared to be a transplant from Ukraine, a commander of security forces that brutally beat students in Kiev in November 2013, sparking a cycle of violent protests that eventually led to the downfall of the country's government.

In an interview at the time, Sergei Kusyuk claimed that his men had been provoked into the bloody confrontation, in which police fired stun grenades and charged protesters with their batons drawn. Later, he reportedly fled to Crimea and, it appears, was one of perhaps 100 former Ukrainian riot police officers accepted into the Moscow riot police unit OMON at the same rank.

The latest protest in Moscow showed the continuation of a political trend that began with similar demonstrations in March: the emergence of a generation of politicized high school and college students demanding accountable government. I met Sasha, 19, and Natasha, 20, on Monday outside a tent featuring traditional Russian snacks and boiled corn. Natasha said she'd been too young to participate in the anti-Putin protests of 2011-2012 but was taking part now because she was angry about living standards in Russia as opposed to the West. Sasha said he wasn't afraid of being expelled from university for attending the demonstration.

Other students, including two 19-year-olds studying at a Russian police academy, said they weren't fans of Navalny but wanted to see change in Russia and were willing to face jail time to take part in the protests. Young people reportedly made up a sizable portion of the more than 1,000 people arrested in Moscow, St. Petersburg and other cities.

Roving teams of riot police in helmets and body armor appeared focused on making arrests, typically diving into the crowd and pulling out protesters carrying signs or other evidence of their opposition to the government. I was knocked over by the crowd during the video I shot below (one rule of covering protests is to try not to get between the front line of protesters and police), but during that interlude, the protester also threw a few punches.

Some scenes of police beating prone protesters were also caught on camera.

At first, it seemed unlikely that the protesters would be able to pull off the rally at all. One opposition blogger told me that Navalny's supporters would probably just "dissolve" into the larger celebration of Russia Day, making it hard to see "who is supporting what."

But protesters gathered near the entrance to the festival, and when one of them yelled, "Putin's a thief," a crowd of people began to cheer, exposing the demonstrators hidden in plain sight.

It was a second strong showing for a political opposition that has been more or less dormant for years.

But not everyone was happy about that.