Between 20,000 and 100,000 people, depending on the report, clashed with police in Moscow on Sunday to protest Vladimir Putin's upcoming presidential inauguration. Dubbed the "March of Millions," Russians chanted "Putin is a thief" to show their displeasure over Putin's return to the presidency. Over 400 people were detained following Sunday's protests, including opposition activists Alexey Navalny, Sergei Udaltsov, and former deputy prime minister Boris Nemtsov. The march turned violent as riot police beat down and attempted to disperse the protestors. Reuters has the number of protestors who showed up for Sunday's rally at "at least 20,000," while Russia's RIA Novosti cites independent estimates that puts the number of protestors between 50,000 and 100,000. 

Reuter's account of the protests paints the picture of a brutal clash between protestors and the riot police: 

Police struck out with batons and hit several protesters on the head as they pushed back a crowd of thousands which advanced towards them holding white metal crowd barriers and throwing objects, Reuters reporters at the rally said.

The demonstrators fought back with flagpoles but police formed a line with riot shields to prevent them moving towards a bridge leading across the Moscow river to the Kremlin.

Riot police waded into the crowd in small groups with arms locked, picking out people and hauling them away, then pushed forward in lines to hem protesters in and disperse them.

The Guardian's isn't much better:

Demonstrators, some carrying anarchist flags and wearing balaclavas, threw flares, and glass and plastic bottles at a phalanx of riot police clad in black helmets and fatigues. Protesters, including pensioners and disabled people, moved forward and shouted at police with cries of "For shame".

Riot police rushed the crowd and flung protesters to the ground before dragging them away. At least two men had bloodied heads after being beaten by baton-wielding officers. Police also fired pepper spray into the crowd. Protesters grabbed officers' headgear, dubbed "cosmonaut helmets" because of their shape, and tossed them into the river or hung them from trees as trophies. One man stood in the middle of the tussle and shouted: "Tomorrow, our state journalists will tell us how correctly the police behaved." Two officers moved in and carted him away.

Russians are mostly angry that the faces in power in Russia have basically stayed the same over the last 12 years. Putin served a maximum two consecutive terms as Russia's president from 2000 to 2008. After, he became Prime Minister as Dimitry Medvedev served a term as president from 2008 to 2012. Putin won this year's presidential election in March, despite widespread rumours of voter fraud, and Medvedev is expected to be named Prime Minister after Putin is sworn in on Monday. Essentially, the two traded jobs. 

After the protests, Dmitry Peskov, one of Putin's spokesman went on Russian state TV and endorsed the police's actions. "From my point of view, the police acted softly," Peskov said. "I'd rather they behave more harshly." 

The opposition leaders arrested during Sunday's protests, Alexey Navalny, Sergei Udaltsov, and Boris Nemtsov, are being detained for "incitement to mass disorder," which could carry up to 10 years in prison.