Five facts on former IS Syrian bastion Raqa

A US-backed alliance of Kurdish and Arab fighters, the Syrian Democratic Forces, said it had fully captured the Islamic State group's former Syrian stronghold Raqa on Tuesday.

Here are five facts about the northern city:

Ancient capital

In an area inhabited since antiquity, Raqa enjoyed a golden age under the early Islamic empire of the Abbasids. 

In 796, the powerful caliph Harun al-Rashid transferred his capital there from Baghdad.

He ordered major works and Raqa was soon dotted with grand palaces and mosques.

Although the caliph's court returned to Baghdad in 809, Raqa remained a major administrative centre for the western part of the empire. 

But in 1258, the city was largely destroyed by the Mongol invasion.

Strategic location

Raqa's location at the intersection of several major roads and the Euphrates River has long made it a key strategic prize. 

It sits 90 kilometres (55 miles) south of the Turkish border and about halfway between Syria's second city Aleppo and the Iraqi frontier.

Before the Syrian civil war, Raqa prospered from agriculture in the fertile valley and benefited from nearby hydroelectric dams generating power for much of the country.

First major city to fall

Two years after Syria's war broke out in 2011, Raqa was the first provincial capital to fall to rebels, including jihadists of the Al-Nusra Front, Al-Qaeda's Syrian affiliate at the time.

But tensions erupted into clashes between Al-Nusra and jihadists from what was to become the Islamic State group.

On January 6, 2014, fierce fighting between the rival groups ended with the predecessor of IS seizing control of the city.

Five months later, Iraq's second city Mosul fell to the jihadists and on June 29, the group declared a "caliphate" across swathes of both countries.

It rebranded itself the Islamic State (IS) and declared its Iraqi chief, Abu Bakr al-Baghdadi, "caliph" of Muslims everywhere.

IS bastion, gruesome theatre

Raqa, home to an estimated 300,000 civilians, became a key IS base for operations in Syria and beyond.

IS took over all levels of civil administration, rewriting school curricula, establishing Islamic courts and creating police units to implement Islamic law.

Raqa was also the scene of some of the jihadists' worst atrocities, including gruesome executions, public displays of corpses and sex slavery.

Coalition target

Raqa has long been coveted by multiple parties to the Syrian conflict, including the government, Russia, Turkey and the US-led coalition set up in 2014 to tackle IS.

On November 5, 2016, the US-backed SDF launched a major offensive dubbed "Wrath of the Euphrates" to seize the city.

A US-led coalition backed them with air strikes, equipment and special forces advisers.

As the SDF closed in on the city, thousands of Raqa residents were smuggled out to territory captured by the US-backed force.

After taking swathes of the surrounding province, including the key town of Tabqa and the adjacent dam, the SDF sealed off the approaches to Raqa from the north, east and west.

In early July, SDF forces penetrated the heavily fortified heart of the city for the first time but continued to face tough resistance from the jihadists.

On September 1, the SDF successfully captured the entire historic district, bringing it closer than ever to the jihadist bastion's well-defended and densely populated heart.

By late September, they had taken control of 90 percent of the city, cornering IS fighters in Raqa's stadium, a few surrounding buildings and a major hospital.

On October 17, an SDF spokesman told AFP that the group's fighters had "taken full control of Raqa" from IS.