The war crimes trial of Congolese former rebel leader Jean-Pierre Bemba has begun at the International Criminal Court (ICC) in The Hague.
The former vice-president of DR Congo denies murder, rape and pillage in the Central African Republic (CAR).
The ICC chief prosecutor says the trial will show that commanders are responsible for their troops' actions.
Mr Bemba - the most high-profile figure to be tried by the ICC since it began its work in 2002 - denies the charges.
The 48-year-old faces two counts of crimes against humanity and three counts of war crimes.
Via his lawyer, he pleaded not guilty to all of the charges as the hearing opened.
Chief ICC prosecutor Luis Moreno-Ocampo told the court that the militiamen who raped and killed hundreds of civilians in CAR in 2002-3 were under Mr Bemba's "effective authority and control".
These atrocities, he added, were not isolated but committed in a "widespread and organised manner".
Mr Bemba, he said, had turned a blind eye to such attacks, and was "even more responsible than his subordinates".
Mr Moreno-Ocampo told the court that its decision would "influence the behaviour of thousands of military commanders" around the world.
At the time of the alleged crimes, Mr Bemba was a militia leader in DR Congo.
His Movement for the Liberation of Congo (MLC) crossed the border from their stronghold in the northern Equateur province into neighbouring CAR to help the president put down a coup attempt.
The defence argues that once MLC forces crossed the border, they were under the control of the CAR authorities.