Millions of people have flocked to the the iconic July 15 Marty's Bridge to mark the first anniversary of the defeated coup.
Having gathered in Beylerbeyi, Çengelköy, Altunizade and Kısıklı districts of the Asian side of the city, people marched to the bridge amid tight security.
The bridge was closed by putschists on the night of the coup attempt and dozens people were killed on it.
The Fetullah Terrorist Organization (FETO) and its U.S.-based leader Fetullah Gülen orchestrated the defeated coup of July 15, 2016, which left 250 people martyred and nearly 2,200 injured.
Ankara also accuses FETO of being behind a long-running campaign to overthrow the state through the infiltration of Turkish institutions, particularly the military, police and judiciary.
Waving large red Turkish flags, tens of thousands joined a national unity march in Istanbul on Saturday, converging at the iconic July 15 Martyrs' Bridge to mark the anniversary of the failed military coup attempt that 250 people died resisting.
The massive crowd, waving flags on the bridge and the highway connecting to it, was filmed with drones. Photographs of the "martyrs" were displayed on monitors on the bridge and their names were also announced.
The Bosporus Bridge, now called the July 15 Martyrs' Bridge, was the scene of clashes between civilians and soldiers in tanks. Some 250 people were killed and more than 2,000 injured across Turkey in the struggle. Thirty-five coup plotters were also killed.
Millions marched to the iconic July 15 Martyrs' Bridge where citizens, heeding a call by Erdoğan to resist the coup, clashed with Turkish soldiers attempting the overthrow.
Crowds on Saturday were massing at the bridge via a major highway that was closed off for the commemorative event.
The authorities have declared July 15 an annual national holiday of "democracy and unity", billing the foiling of the putsch as a historic victory of Turkish democracy.
Millions of Turkish citizens gathered on the Asian side of the Bosphorus in Istanbul to hear a speech by Erdoğan, who earlier arrived from Ankara on his official plane.
Some carried the Turkish flag while others brandished pictures of the "martyrs" who died defeating the coup bid as a sea of people stretched from the bridge, which has since been renamed Bridge of the Martyrs of July 15.
"We are here for the victims, for democracy, for our country for our people and our flag," said Hakan, a resident of Istanbul.
At midnight local time (2100 GMT) people across Turkey will take part in "democracy watches", rallies commemorating how people poured out into the streets.
The scale of Saturday's nationwide commemorations is aimed at etching July 15, 2016 into the minds of Turks as a key date in the history of the modern state.
Giant posters designed by the presidency have sprung up across billboards in Istanbul showing gaudy paintings that portray the key events of the coup night with the slogan "the epic of July 15".
Public transport is free in Istanbul and Ankara over the weekend while mobile operator Turkcell has sent text messages to clients promising them a free extra gigabyte of data from July 15.
Illuminated anti-coup slogans have been hung between the minarets of some of Istanbul's greatest Ottoman mosques.
