People chanted "we want the death penalty!" and some threw nooses towards the suspects. The death penalty has been abolished 2004.
Forty-one of those held were marched into the court outside Ankara one-by-one in a long line in front of television cameras and the public, with each suspect held by two members of the Turkish gendarmerie and flanked by an armed soldier.
People chanted "we want the death penalty!" and some threw nooses towards the suspects. The death penalty has been abolished in Turkey since 2004.
There were also chants of "martyrs don't die, the nation won't be divided". Some people threw water bottles, an AFP reporter said.
Nazan Aytop, who came to court to make sure the blood of the 249 victims of the coup "was not given in vain" said she hoped the "accused will be given the sentence they deserve."
A total of 486 suspects have been indicted in the case and almost all -- a total of 461 -- are held in custody while seven are still on the run and the remainder charged but not in jail.
During the tense opening hearing, veterans and relatives of those killed on the night of the coup bid booed the suspects' lawyers, Dogan news agency reported.
Some lawyers hit tables to protest the "physical intervention" by some of the victims' families as they walked past them, the agency said.
The suspects are accused of running the coup bid from the Akinci air base northwest of the capital, which the authorities regard as the headquarters of the plotters where orders were sent out for fighter jets to bomb parliament.
They are charged with crimes ranging from murder, violating the constitution and attempting to kill President Recep Tayyip Erdogan.
If convicted, they face life imprisonment.
Among the main suspects named in the indictment but still on the run is US-based Muslim cleric Fethullah Gulen, who is accused of ordering the attempted July 15, 2016 putsch.
Gulen, who is based in a secluded compound in the US state of Pennsylvania, strongly denies the charges.
Those held in custody include former air force chief Akin Ozturk who, like several suspects, is also on trial in another case related to the coup bid.
Another chief suspect is theology lecturer Adil Oksuz, whom Turkish officials accuse of being the so-called "imam" of the plot by coordinating the action on the ground in Turkey with Gulen.
Businessman Kemal Batmaz is meanwhile accused of assisting Oksuz.
Oksuz was detained following the coup's defeat, but was subsequently released and is now on the run. Batmaz is in custody in Sincan prison outside Ankara.
Batmaz led the line of suspects into court wearing a cream shirt with black trousers followed by Ozturk wearing a grey shirt and black trousers.
Chief of Staff General Hulusi Akar and other senior commanders were held hostage at the base during the coup attempt before they were freed on the morning on July 16.
The base was seen as the coup bid headquarters where commands were given for the F-16 fighter jets to attack and fly them above the capital.
The Turkish parliament was bombed three times by F-16s.
The trial is taking place in Turkey's largest courtroom established inside a prison complex in Sincan to hear coup-related trials and has space for 1,558 people.
The courtroom has previously hosted mass trials related to the coup bid including one which opened in February of 330 suspects accused of murder or attempted murder.
And in May, 221 suspects were put on trial accused of being the ringleaders of the failed coup.
The attempted coup left 249 people dead, the Turkish presidency says, not including 24 coup-plotters killed on the night.
There was heavy security including 1,130 security personnel inside and outside the courtroom, according to state-run news agency Anadolu, as well as snipers, armoured security vehicles and a drone.
The trial is one of several held across Turkey judging coup suspects, in the largest legal process in the country's modern history.
Over 50,000 people have been arrested over alleged links to Gulen in a wide-scale crackdown under the state of emergency imposed following the coup.