BEIRUT: After more than four years of brutal street fighting and punishing aerial bombardments, the staggering extent of destruction in Aleppo begins to emerge: Tens of thousands of homes and apartments are uninhabitable, most factories have been looted or destroyed and some ancient landmarks have been reduced to rubble.

Reconstruction would likely take years and cost tens of billions of dollars, experts say. Some of Aleppo's centuries-old cultural heritage may have been lost for good. And healing the wounds in a city once split between a wealthier, pro-government west and a poorer, pro-rebel east could take even greater effort.

Damage assessments emerged as the Syrian government announced Thursday that it had assumed full control of the city - a significant victory in a nearly six-year battle with an armed opposition trying to unseat President Bashar Assad. In recent months, rebels rapidly lost ground in the city as Assad and military allies Russia and Iran stepped up attacks.

Located at the crossroads of ancient trade routes, Aleppo was Syria's biggest city before the war, with more than 3 million residents and a world-famous cuisine. It served as the country's industrial hub, home to factories producing textiles, plastics and pharmaceuticals. Its ancient center, recognized as a World Heritage site, drew large numbers of tourists.

Today, Aleppo "resembles those cities that were stricken during World War II," said Maamoun Abdul-Karim, head of the government's museums and archaeology department. The scale of devastation has already evoked comparisons with cities like Grozny and Dresden.

But the destruction isn't spread evenly.

Areas once held by the opposition suffered severe damage after being bombarded for months by Syrian and Russian warplanes. Some eastern neighborhoods look like they have been hit by an earthquake.

In parts of the government-held west, life seemed almost normal. Children attended schools, adults went to work and restaurants and coffee shops were packed. Crude weapons used by the rebels, including mortars and home-made "hell cannons," caused some damage and casualties in government-held areas closer to the front lines.

U.N. satellite images identified more than 33,500 damaged residential buildings in the city, with the most recent photos taken in mid-September, according to a map published this week. A majority of the buildings would have been multi-unit apartment blocks common in Aleppo, said Olivier Vandamme, an official at the U.N. agency that provided the map.

The map indicated that the most intense damage occurred in rebel-held areas. The analysis only considered residential areas and excluded industrial zones. After the images were taken, the Syrian government and its allies intensified bombardments in the final phase of the Aleppo offensive.

A Syrian urban consultant said Aleppo had a pre-war stock of about 550,000 housing units, with a total value of about $50 billion.

The fighting in the city may have caused close to $25 billion in loss of housing, said the consultant, who is involved in data collection and requested anonymity because of what he said was a highly politicized debate over the scope of destruction. About 70 percent to 80 percent of the destruction was in the east, with the rest in Kurdish and pro-government areas, he said.

The consultant estimated that over 60 percent of the homes and apartments in Aleppo are still inhabitable, including those with partial damage. Reconstruction would cost between $35 billion and $40 billion, he said.

Some 250,000 people could potentially return to the devastated east - once home to 1.5 million - and find shelter there by bricking up holes in walls and replacing shattered windows with plastic sheets, he said.

Aleppo's industrial base was largely wiped out, including by looting, the consultant said. Before the war, close to 5,000 small and mid-sized enterprises had industrial licenses in Aleppo, he said.

Exiled business partners Bassam Hajjar and George Saghir, who own a factory for plastic bottles and bottle caps in an industrial zone in northwestern Aleppo, described widespread damage to factories.

"Most of the businesses in the area are destroyed," said Hajjar.

The pair's factory is close to Castello Road, once the main link between the countryside and rebel-held areas in the city. Hajjar said rebels looted his factory, grabbing raw materials, generators and parts of large machinery.

The business partners said it's too risky to resume operations now. Most of the time, there's no electricity and water in the city, they said. The war in Syria continues, as do economic sanctions against the Assad government.

Abdul-Karim, the Syrian government official, declined comment on the damage estimates.

However, he said more than half of Aleppo's fiercely contested ancient center suffered varying degrees of damage. The densely populated area, recognized in 1986 as a UNESCO World Heritage site, contains a 13th century Citadel, a 12th century Great Mosque and ancient markets.

More than 150 buildings in the old city were damaged, Abdul-Karim said. This includes more than half the area of the old markets and parts of the facade of the Great Mosque, whose minaret was destroyed in 2012.

"We need a lot of time and billions of dollars to reconstruct the city," he said, adding that "it will be useless to talk about reconstruction without security and stability."

Repairs at the Great Mosque would be a priority, and Syria will seek UNESCO's help, he said.

A video posted online this week by the Syrian military showed government officials inspecting the damage at the mosque. Small piles of rubble were visible in the courtyard, along with damage to an outer wall.

Mohammed al-Obeid, a senior religious official in the city, said on the video that restorations would begin soon, and that every stone in damaged sections of the mosque has been numbered.

The city's emotional wounds might be harder to heal.

"You had one half of the city trying to go on with life as normal, going out, eating, drinking," said Amr al-Azm, a Syria expert at Shawnee State University in Ohio, referring to the western neighborhoods. "A few meters away (in the east), you had the most appalling conditions, really inhumane conditions."

This rupture "is going to be much harder to heal and will take much longer," he said.