Reuters
WHERE IS ALEPPO?
Aleppo lies in northwest Syria, about 30 miles (50 km) south of the Turkish border. It is at the crossroads of historic commercial routes, 60 miles (100 km) from the Mediterranean Sea to the west and the Euphrates River on the east.
MAJOR EVENTS IN THE WAR FOR ALEPPO
The ancient Silk Road city was spared serious violence for the first year of the war until February, 2012, when a pro-Assad militia killed at least 10 people at a pro-democracy demonstration. By July, rebels had taken control of eastern areas and were battling to extend their reach when the army turned its forces on Aleppo.
In October, 2012, its UNESCO World Heritage listed ancient market was badly damaged by fighting and UNESCO appealed for the protection of Aleppo's listed sites.
The government mounted offensives aimed at encircling the rebel-held east but these have all failed to date. Rebels launched their own offensive on government-held western Aleppo in July, 2015. This also failed.
Since the Russian air force began air strikes in support of the Syrian government on Sept. 30, 2015, the government and its allies have launched offensives against rebels to the north and south of Aleppo and against Islamic State to the east.
Government forces cut the opposition's shortest supply route from Turkey into rebel-held areas in February.
The only route in and out of opposition-held Aleppo is the so-called Castello Road, long a target of government forces. The only road to government-held areas of Aleppo is also vulnerable to attack because it runs close to Islamic State-held territory.
A deal brokered by the United States and Russia to halt the fighting in Syria began to unravel in Aleppo in March, culminating in artillery bombardments and air strikes that have killed about 270 civilians.
WHO CONTROLS WHAT
Aleppo's eastern districts are controlled by an array of rebel groups, many of which receive support from nearby Turkey.
Prominent factions include the Levant Front group, which fights under the banner of the Free Syrian Army. Jihadist groups including the Nusra Front are also active in the Aleppo area and have taken part in battles around the city, often contributing suicide bombers.
Opposition activists say Nusra has little or no presence in the city itself.
The government controls the western districts of the city, including the ancient citadel.
The YPG Kurdish militia controls a district on the northwestern outskirts known as Sheikh Maqsoud. This district is important because of its proximity to the Castello Road.
HISTORY
Aleppo dates from the early second millennium BC. It became a center of Muslim resistance to the Crusaders, who besieged it unsuccessfully in the 12th century.
In 1260 Aleppo was taken by the Mongols, who massacred its inhabitants. After several centuries under the Mamluks, it was in 1516 incorporated into the Ottoman Empire and became the principal market in the Levant.
In the 20th century it became an industrial center to rival the capital Damascus. It is dominated by Sunni Muslims and with a minority population of Christians.
POPULATION
Aleppo was home to more than 2 million people before the war. Today between 250,000 and 300,000 are estimated to live in rebel-held areas. The government-held side of the city is still home to more than 1 million people.