Some were destroyed because they were so closely linked to polytheism. Others were left standing, but turned into the backdrops for gory executions. Others were just the victims of war.
Now, members of UNESCO are trying to see what they can salvage from the Syrian city of Palmyra after so much destruction during 10 months of Islamic State rule. The first job is figuring out what survived. The second is figuring out if it's responsible to resurrect what was lost.
Palmyra's ruins date back to the first three centuries AD, when the city was a powerful centre on trade routes through the Syrian desert. The city linked Persia, India and China with the Roman Empire.
"From the 1st to the 2nd century, the art and architecture of Palmyra married Graeco-Roman techniques with local traditions and Persian influences," UNESCO says.
The city was prised from Islamic State's control four months ago thanks to the combined efforts of Syrian and Russian forces. But much was lost before they could intervene.
The Temple of Bel, the Temple of Baalshamin and the Triumphal Arch are among the many historic buildings and artefacts that suffered severe damage at the hands of Islamic State forces. The head of UNESCO's emergency response unit, Giovanni Boccardi, said in March that the UN cultural organisation provided 2.7 million euros (3 million dollars) of funding for restoration in Syria.
The job is requiring the experts to think outside the box. Using replica replacements of the monumental ruins - a copy of the Triumphal Arch was unveiled at London's Trafalgar Square in April - would serve as a message to the terrorist militia Islamic State: History cannot be erased through terror.
Creating such replicas means using newish technologies like 3D printers to restore the site. One such printer made the arch with Egyptian marble, but it is roughly a third smaller than the damaged original.
To experts, the replica in Trafalgar Square is both a blessing and a curse of modern reconstruction methods. Some experts view these romanticised replicas as a nightmare, comparing them to Disney theme parks.
The reconstruction showed the possibilities and limitations associated with 3D reconstructions, said Markus Hilgert, head of the Museum of the Ancient Near East in Berlin.
He voiced concern about using "cheap reproductions, that are not appropriate at the site."
"They are suitable as monuments showing solidarity and resistance to the destruction of culture, but they are not suitable as a substitute for damaged buildings," he continued.
The good news is that the damage is not as extensive as previously thought. Only 20 percent of the site has been destroyed, according to the first inspection done by Syrian experts.
Mechthild Roessler, director of the division for heritage and the UNESCO World Heritage Centre, said she was relieved that the damage was not as widespread as expected. Some monuments will be able to be reconstructed "relatively easily," including the Triumphal Arch, of which whole pieces remained.
Unfortunately the two temples had been pulverized, she said.
Roessler was part of an expert delegation that visited the site in April after it was liberated from Islamic State to assess the extent of the damage. The ongoing civil war made it one of her most difficult missions, she said.
Many of the sites could only be viewed from a distance because Islamic State placed landmines throughout the city before fleeing. The Russian army has removed at least 4,000 mines from the area, Roessler said.
Despite Russia's efforts, Palmyra isn't safe enough for the experts to work there. And for those involved in deciding Palmyra's fate, one thing is certain: A thorough and detailed assessment of the damage is needed.
As a rule, "reconstruction is not allowed within the framework of the World Heritage Convention," Roessler said.
Other possible restoration efforts without the use of replicas could include virtual simulations on smartphones, projections or a documentation centre.
Beyond the logistics of restoring the site, the debate is further complicated by political factors. Syrian President Bashar al-Assad has a vested interest in restoring the heritage site as quickly as possible. Doing so would symbolize strength and power over the war-torn country. That leads to suspicion among members of UNESCO's World Heritage Committee.
"Neither should we forget the responsibility of the Syrian regime in the destruction of the heritage of its own country," said Laurent Stefanini, France's representative.
Stefanini wants to ensure that work carried out by UNESCO to restore Palmyra is not instrumentalized by the Syrian regime in Damasus. Especially when you remember that the ancient city of Aleppo, also a UNESCO world heritage site, is regularly the target of Syrian airstrikes.