Fifteen people went on trial in the Moroccan capital on Friday over the theft of dozens of luxury watches belonging to King Mohammed VI.
Defence lawyers said the suspects, arrested at the end of last year, were also charged in a Rabat court of forming "a criminal gang".
The main suspect is a 46-year-old who worked as a cleaning woman in a royal household and has allegedly confessed to the robberies, while the others have denied involvement.
The woman, who is alleged to have stolen 36 watches, had many of them melted down and sold on to gold merchants.
The 14 others in court, all men, are gold traders or intermediaries who said they had no knowledge of the robberies.
Forbes magazine in 2014 classified the 56-year-old monarch as one of the world's richest men with wealth estimated at more than $2.5 billion.
He has a taste for luxury cars, paintings and watches, and was shown in an Instagram post in September 2018 with a Patek Philippe diamond-encrusted watch in white gold with an estimated value of $1.2 million.