ISTANBUL, Turkey (CNN) -- Two years ago, the Syrian revolution erupted with a full-throated scream of defiance. After years of repression, it shocked even those who were doing the screaming.
"The first protest was so great when we screamed and said 'the people want to overthrow the regime,'" recalled Media Daghestany, an opposition activist and single mother of one from the Syrian city of Homs.
"I screamed, and then went silent to hear, 'Oh, I said that.' And then I screamed again," she said.
For truck driver Abu Mariam, his evolution into an opposition activist occurred after he witnessed Syrian security forces beating demonstrators in Aleppo, the nation's largest city.
"I saw protesters were screaming, "God is great," and they were being stabbed with knives and beaten with electric clubs," Abu Mariam said.
"Automatically, I joined them and started screaming 'God is great.' When I yelled that, I felt like was reborn."
The popular unrest following the first protests in March 2011 has challenged the dynastic dictatorship that has ruled Syria for years.
Today, Syria is being torn apart by a civil war that has killed more than 70,000 people and forced more than one million Syrians to flee the country. The conflict threatens to spill across borders to destabilize neighbors in an already turbulent Middle East.
The opposition says today marks the second anniversary of the beginning of the uprising.
"Of course, if the revolution was won in the first six months, everything would be easier," Daghestany said, while toying with a necklace decorated with the colors of the Syrian rebel flag.
Daghestany and Abu Marian are two activists who led protests in two different cities at the start of the revolution. Neither of them expected that the uprising would unleash so much bloodshed and carnage.
Since 2011, their lives have taken unexpected turns, even as Syria itself has undergone violent transformation.
Amateur videos from 2011 show Daghestany dressed in a Che Guevara T-shirt with a bandana wrapped around her face, leading small crowds of women chanting for the overthrow of the Syrian government.
For Daghestany, leftist dissident politics were part of her family's DNA.
"I was against the regime before the revolution. My dad was in prison for eight years and I grew up in a family which hated the regime, the father and the son," said Daghestany, referring to Bashar al-Assad, who inherited the presidency from his father, Hafez, who died in 2000.
Abu Mariam came from a more modest background. He was a truck driver who shipped cargo between Aleppo and neighboring Turkey.
I know that the choice now is better than if we didn't have any revolution.
He said he became an opposition leader after security forces threw him in prison.
"They arrested me at a demonstration to honor the martyr Omar al Hawi," Abu Mariam said.
"In the central jail, I met with many Syrian rebels and we started coordinating together. We talked about why my neighborhood, Bustan al Kaser, wasn't participating in the uprising. When I was released I started working with other activists and arranging demonstrations in Bustan al Kaser."
Abu Mariam is featured prominently in activist videos, chanting into a megaphone, at the head of hundreds of flag-waving demonstrators gathered in Aleppo's narrow streets.
The security forces cracked down hard, with waves of arrests, systematic use of torture and repeated use of deadly force. By the summer of 2011, the United Nations was reporting that more than 2,200 people had been killed. A trickle of Syrians refugees had begun fleeing across international borders.
Citing a pattern of widespread, systematic human rights abuses, U.N. Human Rights Commissioner Navi Pillay said the Damascus regime may have been guilty of "crimes against humanity."
As the death toll mounted, some activists began arming themselves. The rebels referred to themselves collectively as the Free Syrian Army. Their ranks were bolstered by soldiers and officers who defected from the Syrian military and security forces.
After a year of bloody fighting, rebels succeeded in pushing the Syrian military back from many towns and villages, particularly in the north of the country.
With the exception of Aleppo, which is divided between loyalists and insurgents, the government still maintains its hold on Syria's largest cities. It has resorted increasingly to airstrikes, artillery barrages and surface-to-surface missile attacks to reach rebel-held areas where loyalist ground troops no longer operate.
Syrian Deputy Foreign Minister Faisal al-Maqda, in an interview last month, said the government will win the war. Al-Maqdad defended the regime's shelling, calling it a reaction to the opposition's violence.
"This is not our option," he said. "This is the option they imposed on us to defend our own people and our own cities. What we are demanding is a stop to all these actions and to come to the table where we discuss all our grievances together."
Meanwhile, the rebels have evolved both militarily and ideologically. They profited from the capture of long stretches of border with neighboring Turkey. Turkey has provided a pipeline for smuggled weapons, ammunition and foreign volunteer fighters.
As the conflict dragged on, hardline Islamist groups have surged to the forefront of the armed rebellion. One group in particular, an Al Qaeda-linked movement labeling itself the Nusra Front, claimed responsibility for devastating car bombs that killed government officials and innocent bystanders in the Syrian capital.
"During the peaceful demonstration days, I was one of the people who did not know who the Nusra Front was," said Abu Mariam. "We had one revolution and one revolutionary flag. But when we started getting weapons, when the Nusra Front came here, divisions started emerging between the people."
Two years in to the revolution, Abu Mariam still lives in his neighborhood of Bustan al Kaser in the divided city of Aleppo. In an increasingly bombed-out city with hardly any electricity or fuel, Abu Mariam and his followers continue to organize protests and struggle to distribute humanitarian assistance to the growing ranks of desperate Syrians.
But it is clear that the truck driver-turned-activist has a hard time recognizing the opposition movement he once embraced.
Twice in four weeks, Abu Mariam said he had been beaten by anti-government rebels.
Last February, fighters from an Islamist court led by the Nusra Front briefly detained Abu Mariam.
"The Sharia Authority of the Nusra Front and other Islamist brigades...accused me of protesting against the caliphate," Abu Mariam said, during a short phone interview after his release last February.
"They flogged me 10 times."
A photo posted by Abu Mariam on Facebook showed his back covered with angry red welts.