A former Turkish army chief and more than 100 others have gone on trial accused of plotting to overthrow a pro-Islamist government in 1997.
Prosecutors have called for General Ismail Hakki Karadayi to face a life sentence.
He is suspected of helping what became known as the post-modern coup, as no soldiers were involved.
Prime Minister Necmettin Erbakan was forced to resign in 1997 and was replaced by a civilian government.
A number of serving and retired generals linked with Mr Erbakan's removal from power were charged last year while Gen Karadayi was charged more recently
Another former armed forces chief, Gen Ilker Basbug, was one of dozens of people convicted of involvement in a more recent plot, known as Ergenikon. He led the army until 2010 and was jailed for life last month.
That alleged conspiracy was said to have been aimed at toppling the current government of Prime Minister Recep Tayyip Erdogan's Justice and Development Party (AKP).
Critics cast doubt on the evidence for the allegations and accused the government of trying to silence its secularist opponents.
Turkey's military has long seen itself as the guarantor of the country's secular constitution, analysts say.
Necmettin Erbakan's government was forced to step down on 28 February 1997, after a meeting of the National Security Council, and his Welfare Party was later outlawed.
Gen Karadayi denies that he played any part in alleged army interference in politics.
However, his deputy at the time, Gen Cevik Bir, disagrees and has insisted during all the investigation that he was simply following Gen Karadayi's orders.
Gen Bir was also being tried on Monday.
Investigations continue into other alleged coup plots involving the military.
It staged three coups between 1960 and 1980 and has a history of tension with Mr Erdogan and his party.
The Islamist-rooted AKP, in power since 2002, emerged from the Welfare Party.
Last year, a Turkish court sentenced three former army generals to 20 years in jail each for plotting another coup. More than 300 officers were convicted of involvement in the plot.
They were accused of plotting to bomb mosques and trying to trigger a war with Greece in order to justify a military coup against the elected government of Mr Erdogan in 2003.