Here are five facts about the northern city which has been roughly divided into a regime-controlled west and a rebel-held east since July 2012 and is currently undergoing a brutal siege which experts say could prove a turning point in the conflict:
- Aleppo enters the war -
In April-May 2011, thousands of students demonstrated in Aleppo, which had so far been spared the unrest in Syria since mid-March.
While the student protests were brutally crushed, rebels took control of several parts of Aleppo province which they would later use as launch pads for a massive July 2012 offensive on the city.
The army fought back with tanks, leaving Aleppo divided into east and west.
The first air strikes in Syria's war followed.
Since then, Aleppo has been split between zones controlled by the rebels and those by the regime, with its province divided up between regime, rebels, jihadists and Kurds.
- A devastated city -
The once-flourishing city with its globally-renowned old town has been reduced to a site of devastation.
Since December 2013, the army has been using brutal barrel bomb strikes from helicopters and military planes, targeting opposition-held residential neighbourhoods, according to the Syrian Observatory for Human Rights and militants.
Use of this particularly destructive weapon has been denounced by the United Nations and international non-governmental organisations.
Rebels have retaliated with deadly rocket fire on regime-held neighbourhoods.
Medics say that health conditions in the rebel part of the city, where several hospitals have been hit, are alarming and that medical staff are falling victim to the regular bombardments.
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- "Disastrous" siege -
Since July 17, Aleppo's rebel neighbourhoods, home to some 250,000 people, have been totally under siege, after regime forces cut off the last supply route.
The noose has since tightened for the inhabitants, faced with food and petrol shortages and soaring prices.
On Thursday, Russian Defence Minister Sergei Shoigu said Moscow had launched a "large-scale" operation together with the Syrian government to open humanitarian corridors for civilians and fleeing fighters.
France's ambassador to the United Nations, Francois Delattre, has compared Aleppo's plight to that of Sarajevo during the Bosnia war.
- An ancient city -
Provincial capital Aleppo is one of the world's oldest cities to have been constantly inhabited since at least 4,000 BC, thanks to its strategic position between the Mediterranean and Mesopotamia, present-day Iraq.
The manufacturing centre, renowned for its textiles, is situated at the crossroads of major trading routes, and numerous civilisations succeeded each other on its soil.
Listed as a UNESCO World Heritage site in 1986 Aleppo's citadel, a jewel of Islamic military architecture in the Middle Ages, was built over three centuries from the 10th century.
It was damaged by a blast in July 2015. Two years earlier, fighting destroyed the minaret of the Ummayad mosque and before that a fire ripped through the ancient souk, partially destroying it.
- A major stake in the conflict -
The control of Aleppo is one of the major stakes in the Syria conflict and the army has made its conquest one of its priorities.
Experts say the army's advance, backed by Russian air power, is a body blow to the rebels and could be a turning point in the overall conflict.
"Apart from the humanitarian disaster, the recent events in Aleppo are very important politically-speaking," Karim Bitar from the French think-tank IRIS said.
"Deprived of oxygen, the rebels are faced with an impossible mission," he said, while President Bashar al-Assad is "considerably more at ease than several months ago."