Former commander of the Turkish Air Force Akın Öztürk, who has been accused of masterminding the coup, will stand trial. Other high-profile defendants include Ali Yazici, Erdogan's former personal military aide, and Levent Turkkan, the former military aide to Turkish Armed Forces commander Hulusi Akar.
Out of the 209 total, one four-star general (Öztürk), three three-star lieutenant generals, four two-star major generals, 16 one-star brigadier generals, and three rear admirals will stand trial.
The suspects were paraded through the streets of Ankara as pro-government demonstrators barraged them with jeers. Some of them threw nooses at the accused as a symbolic call for the reinstatement of the death penalty.
Capital punishment was outlawed in Turkey in 2004 as part of a push to join the European Union, but Erdogan claimed that he would renew the death penalty after the coup if parliament or a public referendum wills it.
"We want the death penalty, we don't want them to be fed and housed here. We want these traitors to be buried without any flag," protester Cengiz Ozturk told Al Jazeera.
"I am here to settle the score with terrorists, I am here to show that I stand by my people, my flag, and my religion," said another protester, Mehmet Yaman, to Reuters. "I am here to show the terrorists that we will stand firm. I want them sentenced to death in a fair trial, I want the traitors of this country to be punished."
Öztürk led the procession of prisoners, who have been accused of "violating the constitution," "using coercion and violence in an attempt to overthrow" the Turkish government, "martyring 250 citizens" and "attempting to kill 2,735 citizens," according to Turkish newspaper Hurriyet.
Anadolu, the Turkish government's news agency, reported that approximately 1,500 personnel would be providing security during the trial, which is expected to last through June. Armored vehicles, rooftop snipers, and overhead drones were all part of the procession.
Twelve of the 221 being charged will be tried in absentia, most notably Fethullah Gulen, preacher and Erdogan's former right-hand-man who became one of his most bitter enemies following their 2013 falling-out. Gulen, who lives in exile in the United States, has been accused of masterminding the uprising. He denies the charges.
More than 47,000 people have been arrested in Turkey for having suspected ties to either Gulen or the "Peace at Home Council," which attempted to overthrow Erdogan's government in July 2016.
"Fundamental rights and freedoms, as well as the secular democratic legal structure based on the separation of powers, have been abolished by the heedless, misguided and even treacherous president and government officials," the Council said in a statement during the failed coup.
Another 100,000 individuals have lost their jobs as a result of their alleged involvement in the coup, more than half of them in law enforcement or education.