Kemal Kilicdaroglu, leader of the opposition Republican People's Party (CHP), finished the last kilometer of his long trek alone and was met with huge applause and chants of "Rights! Law! Justice!" as he entered Maltepe Square.
The square was packed to its seams and many attendees and marchers gave up trying to enter the rally, instead joining in on the chants from grassy patches outside the square.
"We need justice and democracy. That's why we have been in the roads for days," said Fadime Özbudak, a 47-year-old housewife. "It's wonderful here. I couldn't even get inside, but I'm just so happy. ... I've never seen anything like this in Turkey."
"I'm here for justice, rights and rule of law. I believe everyone needs justice. Some of the wrong policies need to end. Everyone knows what they are. We want a livable Turkey. The poor get poorer while the rich get richer," she said. "The people say no to these injustices. This is the voice, the scream of the people for justice."
It's not clear exactly how many people Kilicdaroglu addressed in and around the square, but the crowd was enormous. While some estimates pegged the tally at more than a million people, that number could not be immediately confirmed.
The "March for Justice" has mushroomed from a one-man protest
led by Kilicdaroglu. He soon was joined by throngs of disaffected citizens -- many angry with President Recep Tayyip Erdogan -- as Kilicdaroglu kept his promise to walk from the capital, Ankara, to Istanbul after the imprisonment of one of his party's parliament members.
Huge demonstrations unfolded in Maltepe, a district in suburban Istanbul that is home to the prison where Enis Berberoğlu is being held. They waved Turkish flags and banners bearing the word, "adalet," or "justice," and held up portraits of Turkey's founding father Mustafa Kemal Ataturk.
Berberoğlu was arrested and sentenced to 25 years in jail for giving an opposition journalist video allegedly showing Turkey sending weapons into Syria.
"Turkey has stopped being a democratic country. It has become beholden to one man," Kilicdaroglu told CNN. "This we cannot accept."
Still reeling from coup attempt
The rally comes almost a year after a failed military coup radically changed the country's direction
. Following the coup attempt, Erdogan and his government have clamped down on civil liberties across the country, gutted public institutions and universities, heavily restricted the media and ordered mass arrests of activists, journalists and the political opposition.
The country has remained in a state of emergency for almost a year now, giving the Erdogan-led government extraordinary powers to detain anyone it sees as oppositional.
Among the marchers was 62-year-old Refika Ozturk, a retired municipality worker who walked for 10 days. She sat on a grassy patch in Istanbul, exhausted, her shoes off. She and her friends wore T-shirts that read "adalet."
"I'm marching for my rights, the law and justice. You can do something as hard as walking like this for so long when you believe in it, when it's for a cause," she said Saturday.
What will come of rally?
Despite the fatigue, the final leg to Istanbul was festive, with bands playing along the way.
Turkish protesters have regularly clashed with security forces over the past year, but the march has been peaceful, with police securing the protest from outside threats.
It's unclear whether that harmony will continue in Istanbul, a city at the heart of Turkish liberalism, where rallies are now banned in historic Taksim Square.
At least one protester who spoke to CNN wondered if the government would hear protesters' demands, forget the rally or dub the demonstrators terrorists once the flags were gone and the chants had died down.
The long walk to Istanbul was difficult for many. Two people suffered cardiac arrests, one of whom later died, while others found the heat unbearable and rushed for water and shade at every opportunity. On other days, torrential rain was the enemy.
No shortage of Erdogan backers
The protest is a sign that Turkey remains divided. While the march was cheered by onlookers, Erdogan's supporters also turned out to watch the protests, chanting his name in response to the marchers' chants of "Rights, law, justice."
Supporters of the protest drove by and made the peace, or victory, sign. But Erdogan supporters flashed the four-finger Rabia sign, originally used in support of Egypt's Muslim Brotherhood but since adopted by Erdogan's fans.
The division has persisted for some time. In April, Erdogan was granted sweeping powers after narrowly winning a referendum that transferred powers from parliament to the executive branch of government. The presidency in Turkey is traditionally ceremonial, but Erdogan has acted as the nation's leader and its head of government. International monitors slammed the referendum for being conducted on an uneven playing field.
Kilicdaroglu has tried to brand his protest as beyond politics. His supporters have displayed no political logos, and he has called for Turks of all political affiliations to join.