As part of the commemoration, Turkish President Recep Tayyip Erdogan flew to Istanbul today and was photographed waving at a fighter jet escorting his aircraft. He is to join the crowds later and unveil a Martyrs' Memorial to honor those who died opposing the coup. Marches and events are also taking place in Ankara, the capital.
Earlier in the day, Prime Minister Binali Yildirim spoke at a special parliamentary session in Ankara attended by Erdogan.
Turkish soldiers attempted to overthrow the government and the president using tanks, warplanes and helicopters on July 15, 2016.
The coup plotters declared their seizure of power on the state broadcaster, bombed the country's parliament and other key locations, and raided an Aegean resort where Erdogan had been on vacation.
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But Erdogan had already left and the coup attempt was put down by civilians and security forces.
The Bosporus Bridge, now called the July 15 Martyrs' Bridge, was the scene of clashes between civilians and soldiers in tanks.
Yildirim thanked the thousands who heeded a call by Erdogan to flood the streets to resist the coup.
"We are able to come together again here today because of our 250 heroic martyrs, 2,193 heroic veterans and the great Turkish people. Your country is grateful to you," Yildirim said.
In the aftermath of the coup attempt, Turkey declared a state of emergency that has been in place ever since, which has allowed the government to rule by decree and to dismiss tens of thousands of people from their jobs.
Gulen has denied the allegations.
In the latest government decree published yesterday evening, 7,395 more state employees were fired, including teachers, academics, military and police officers, bringing the number of dismissed to more than 110,000.
The government calls the crackdown necessary to purge state institutions of those linked to Gulen, but critics say the dismissals are arbitrary and the victims' paths to recourse severely curtailed.