Ukrainian film director Oleg Sentsov has gone on trial in the southern Russian city of Rostov-on-Don accused of plotting terrorist acts in Crimea.
He was arrested weeks after the Ukrainian peninsula was annexed by Russia in 2014.
Mr Sentsov denies the charges against him and his cause has been taken up by other directors, including Mike Leigh, Stephen Daldry and Pedro Almodovar.
If found guilty, he could be jailed for up to 20 years.
The Ukrainian government says Mr Sentsov, best known for his 2011 film Gamer, is a political prisoner.
He has also attracted support from celebrated Russian film director Nikita Mikhalkov, who has close ties to President Vladimir Putin and has openly backed Russia's annexation of Crimea.
Mr Sentsov, 39, is one of a number of a Ukrainian figures held by Russia. Military pilot Nadiya Savchenko is also facing trial in southern Russia accused of killing two people.
Both have been described by the US as Ukrainian hostages held by Russia.
Ms Savchenko says she was abducted by pro-Russian rebels on Ukrainian territory and handed to the Russian authorities.
Her lawyer said she had been moved to the Rostov region pending her trial.
Oleg Sentsov went on trial on Tuesday alongside Ukrainian activist Alexander Kolchenko at the North Caucasus military court in Rostov-on-Don.
"I don't consider this court a court at all, so you can consider whatever you want," he told the court, according to the AFP news agency.
Mr Sentsov is accused of organising a terrorist group and planning terrorist attacks in Crimea. Prosecutors say he was involved in two attempted arson attacks in the city of Simferopol, ordered by extremist Ukrainian group Right Sector.
The case against Mr Sentsov is primarily based on evidence given by two men who have already been convicted and given seven year jail terms.
Mr Sentsov insists the trial is politically motivated, arguing that he was beaten in jail for 24 hours in an attempt to force a confession.
But investigators refused to open a case on his allegations of torture, suggesting that his bruises were self-inflicted and that he was keen on sado-masochism, Sentsov's lawyer said.