A defence lawyer for Prince Heinrich XIII of Reuss denied his client was the ringleader of a far-right plot to violently overthrow the German state.
Prince Reuss, a 72-year-old businessman whose title holds no formal weight, went on trial before the Frankfurt Higher Regional Court on Tuesday along with eight others.
"He is not a leader, not a ringleader, and he is also not a member of a terrorist organization," said lawyer Roman von Alvensleben.
The initial focus on the first day of the trial was clarifying procedural issues. The trial continued in the afternoon with the reading of the indictment.
The defendants are accused of being members of the "Reichsbürger" network, which prosecutors call a terrorist organization.
So-called "Citizens of the Reich" believe that the modern German republic illegitimately replaced the German Reich that was founded in 1871 and continued under the Nazi regime until 1945. They reject the legitimacy of Germany's modern federal state and its laws.
The plan, prosecutors allege, was for members of the group's paramilitary wing to raid parliament, arrest politicians and ultimately install Prince Reuss as Germany's new leader.