A dozen leaders of Catalonia's failed 2017 independence bid have gone on trial in Madrid, facing charges including rebellion and sedition.
If convicted, some could face up to 25 years in prison.
The semi-autonomous region of Catalonia held an independence referendum on 1 October 2017, and declared its independence from Spain weeks later.
But Spanish authorities declared the vote illegal, and the national government imposed direct rule.
The Catalonia crisis is considered the most serious to hit Spain since the era of fascist dictator Francisco Franco, who died in 1975.
Nine of the defendants have spent months in pre-trial detention, and arrived at the court on Tuesday morning under guard. The remaining three had been free on bail.
The most high-profile of the Catalan leaders on trial is former Vice-President Oriol Junqueras. His superior - former President of Catalonia Carles Puigdemont - fled abroad and remains in exile.
Mr Junqueras faces the longest potential sentence for the alleged crime of rebellion, at 25 years. Others accused of the same charge, including former speaker of the Catalan parliament Carma Forcadell, could receive sentences of 16-17 years.
They also face the lesser charge of sedition, as do several former ministers.
There is also the accusation of misuse of public funds, in organising a referendum that had been declared illegal by Madrid.