In all, the Syrian Center for Policy Research (SCPR) estimates 470,000 Syrians have died and 1.9 million people had been wounded during the war, while life expectancy plummeted from 70 years in 2010 to 55.4 years in 2015.
So today marks a grim anniversary.
Here is a timeline of some of the major events over the course of the conflict, now entering its sixth year.
2011: The uprising
Deraa, known as "the cradle of the uprising," was the first city in Syria to revolt against President Bashar al-Assad on March 15, 2011. Assad's security forces moved in quickly to quash the protests, shooting and killing dozens of demonstrators.
But the violence only fueled more protests, which spread to cities across Syria. Demonstrators called for Assad's ouster.
The regime continued cracking down on what it called "an armed rebellion" by radical Islamists, and pro-regime demonstrators turned out in the streets of Damascus in support of Assad.
But the U.S., Britain and France condemned the regime's repressive tactics.
The first refugees began to flee from the violence in Syria and head for neighboring countries.
The situation then spiraled into conflict.
2012: Full-blown war
The chaos spiraled into all-out war as Syrian forces stepped up their bombardment of towns controlled by anti-Assad groups.
Moderate rebels of the Free Syrian Army declared to fight government forces in a battle for the capital, Damascus, which they ultimately lost.
They then launched an offensive in the northern city of Aleppo, which was divided between controlled districts in the east and regime-held areas in the west.
The conflict grew more complex by the day, as new armed groups entered the fray. Hezbollah said it sent fighters to back Assad's forces, and they then went on the offensive.
2013: Chemical weapons
Hundreds of Syrians were killed in what Western governments allege was chemical weapons attacks by Assad's regime targeting rebel-held neighborhoods near the capital of Damascus.
The U.S. warned it may launch airstrikes if chemical weapons were used again.
On Sept. 14, the U.S. and Russia agreed on a plan to eliminate Syria's chemical weapons.
The number of Syrian refugees then skyrocketed and the war deepened.
2014: The fall of Homs, the rise of ISIS
In May, the rebel-held city of Homs fell to the Syrian regime after a fierce two-year siege.
Meanwhile, Assad won re-election in polls dismissed by many around the globe as a farce.
At the same time, a new and brutal force emerged in the war. The group called itself the Islamic State of Iraq and Syria (ISIS), and declared a "caliphate" in territory that spans from Aleppo to Iraq.
ISIS seized control over all of Raqqa province and made the city its de facto capital.
The group ruled with an iron first and began to carry out gruesome executions of those who don't conform to its radical ideas. The victims included Western journalists, such as James Foley, who is executed in August.
In September, the U.S. and five Arab countries join forces and launch airstrikes against ISIS around Aleppo and Raqqa.
2015: Refugees and Russia
Syria's Al-Qaeda affiliate, al-Nusra Front, backed by rebel allies, seized most of the northwestern city of Idlib. Over the summer, Assad and his forces lost more and more ground to rebel groups.
On Sept. 30, Russia came to the aid of Assad, launching airstrikes against his opponents in Syria, including ISIS.
But Moscow was soon accused of bombing civilian neighborhoods and killing hundreds, including women and children.
Meanwhile, hundreds of thousands of refugees fled the war-torn country. Most went through Turkey and then by boat to Europe. They joined other refugees and migrants escaping war and poverty, spawning the largest migrant wave since World War II.
2016: Siege and a ceasefire
Backed by Russian bombs, Assad is more confident than ever. On the offensive, his forces make battlefield gains, including around Madaya and the strategic city of Aleppo, a rebel bastion.
His assault forced tens of thousands more to flee to the Turkish border and raised fears of another brutal siege.
Assad's forces have the city nearly surrounded when international governments, with much difficulty, convene peace talks in February.
On Feb. 27, a "cessation of hostilities" came into force. Brokered by the U.S. and Russia, it applied to Assad's forces and those of moderate rebel groups fighting them. But it did not apply to ISIS and al-Nusra Front, which together controls more than half of Syria's territory.
Fighting continued, but with much less intensity.
On March 15, Russia announced it will withdraw its troops from Syria, saying it has accomplished its goals of shoring up Assad's regime and protecting its interests in the Middle East.
Meanwhile, peace talks led by the United Nations get underway again in Geneva. For the first time in five years of war, there are signs of hope that ending the war is possible.
Have something to add to this story? Share it in the comments.