After IS, Mosul rebuilds monuments, mosques -- and society

* Mosul known for its diversity before IS takeover

* Monuments and mosques that defined Mosul in ruins

* Many residents are too scared to return

By Stephen Kalin

MOSUL, Iraq, July 26 (Reuters) - Faisal Jeber arrested and interrogated suspected Islamic State militants during the battle for Mosul. Now he is taking up a new fight that could be just as crucial to the city's future.

The 47-year-old geologist is trying to restore historical sites damaged during the militant Islamist group's brutal three-year rule over the northern Iraqi city.

By piecing back together buildings which he says gave Mosul its soul and identity before the war, Jeber hopes also to help rebuild its social fabric.

But the city's renaissance could take a generation, if it happens at all, he says, and it is uncertain how Mosul and other Iraqi towns and cities recaptured by government forces will look afterwards.

How Mosul's identity is reconstituted will help determine whether Iraqi leaders can pacify a country dogged by jihadists and sectarian bloodshed for the past decade.

"ISIS (Islamic State) tried hard to destroy Mosul's identity by demolishing everything and making it monochrome," Faisal told Reuters in Mosul. "I am using this to unite my city and then maybe the whole country."

Before the war, Mosul was Iraq's second-largest city, known for its diversity, religious conservatism and nationalism. After the U.S.-led invasion that toppled Saddam Hussein in 2003, it became a base for al Qaeda and the Sunni insurgency.

Since IS seized Mosul in 2014 in the face of the Iraqi army's collapse, the militants have blown up monuments, evicted communities that had lived together for centuries and turned neighbours against each other.

Following the group's defeat in Mosul this month in a U.S-backed offensive, billboards have gone up on a main road hailing the city as the cradle of civilisation and showing landmarks dating back to the days of Mesopotamia.

It is, Jeber says, a unique moment to rebuild Mosul's multicultural identity and combat radical Islamism.

"It's an opportunity and it's just the right time to do it because if you talked to any Mosulawi about that before (IS), nobody would accept it. But now people came out of a radical Muslim experience, they are in shock," he said.

"Either we do it this year and we use this opportunity or else we lose it forever. We have a very narrow window."

"FOUR LEVELS OF CIVILISATION"

Jeber was detained by IS in 2014 on suspicion of spying and threatened with execution, but escaped and went on to use his knowledge of Mosul to help Iraqi forces target the insurgents.