Here is a look at the alleged "Ergenekon" conspiracy to overthrow the government of Prime Minister Tayyip Erdogan:
* The alleged network of secularist ultra-nationalists draws its name from a mythical Central Asian valley where Turks are said to have been saved from annihilation by a wolf that led them past their enemies to freedom.
* The Ergenekon network was said to have been linked to the "Deep State", militant secularists in key areas of the Turkish establishment who are believed to have wielded considerable influence in political life in recent decades.
* The investigation was initially spurred by seizure of 27 hand grenades in a police operation at a house in Istanbul's Umraniye District in June 2007.
* There are 275 defendants, 66 of whom are still held in custody, and the case has included 23 indictments. Former armed forces chief General Ilker Basbug is among those accused of involvement in Ergenekon.
* Opposition members of parliament, academics, politicians and journalists are also among those on trial.
* Prosecutors in March sought life sentences for 64 of the defendants and sentences of up to 15 years for another 96 defendants.
* Prosecutors charge that the network planned assassinations and bomb attacks to stir up unrest and pave the way for a military coup. The military has denied any link to such a group. The arrests of retired generals and serving officers was unprecedented in Turkey, where the army has long enjoyed an untouchable status because of its popular support.
* Last September a separate court in Silivri sentenced more than 300 military officers to jail for plotting to overthrow Erdogan in 2003 in the "Sledgehammer" case. It handed prison terms to 322 serving and retired army officers and acquitted 34.
* Those sentenced to life included retired generals Cetin Dogan and Halil Ibrahim Firtina, and retired admiral Ozden Ornek, considered the ringleaders of the plot.
* The "Sledgehammer" conspiracy is alleged to have included plans to bomb historic mosques in Istanbul and trigger conflict with Greece to pave the way for an army takeover.
* The military was for decades viewed as the guardian of Turkey's secular establishment, launching three coups between 1960 and 1980 and pressuring an Islamist-led government to quit in 1997.
* Erdogan's Islamist-rooted AK Party, which came to power in 2002, tamed military influence over policy-making and ministerial appointments as part of EU-backed efforts to strengthen democracy.
(Reporting by Daren Butler and David Cutler, London Editorial Reference Unit; Editing by Nick Tattersall and Giles Elgood)