ISIS destroys Arch of Triumph in Syria's Palmyra ruins

                                                         
militants have destroyed the iconic Arch of Triumph in Palmyra, the latest cultural treasure of the ancient site that they have reduced to rubble, Syrian authorities said.

The 1,800-year-old monumental arch, which framed the approach to the Roman city, was blown up Sunday, Syria's Directorate General for Antiquities and Museums said, citing witnesses in the local community.

ISIS jihadists seized control of Palmyra, a UNESCO World Heritage Site, and the surrounding area from Syrian government forces in May. Since then, the Islamic extremists have beheaded the antiquities expert who looked after the ruins and set about demolishing their architectural riches.

In August, they leveled two temples of immense cultural significance -- the Temple of Bel and the Temple of Baalshamin -- prompting outrage and condemnation from around the world.

The Arch of Triumph, consisting of one large arch flanked by two smaller ones, opened onto Palmyra's elegant Colonnade. The top of the arch was decorated with "beautiful geometrical and plant ornaments," the Syrian antiquities directorate said.

UNESCO calls destruction 'war crime'

UNESCO, the United Nations cultural organization, describes the archway's adornments as "an outstanding example of Palmyrene art."

The organization's director general has called ISIS' destruction of Palmyra's architectural gems "a war crime."

As well as the temples, the terrorist group has also demolished Roman-era funerary towers that were "among the most representative and evocative monuments" at the site, UNESCO said last month.

The militants, however, are unapologetic over their step-by-step trashing of one of the world's most important ancient sites, publishing photos of some of the destruction.

Palmyra, northeast of Damascus, is known as the "bride of the desert" for its magnificent collection of structures along a historical trade route that once linked Persia, India and China with the Roman Empire.

'Cultural carnage'

The Syrian antiquities directorate said it was increasingly worried about Palmyra's fate under the extremists, noting the ancient city "stands for of tolerance and multicultural richness, the things ISIS hates."

The militants have also smashed up other antiquities in the parts of Syria and Iraq that they control.

Markus Hilgert, director of Berlin's Pergamon Museum, one of the pre-eminent museums for ancient Middle Eastern artifacts, said he was "extremely troubled by the fact that the international community of governments and cultural heritage professionals appears to be unable to stop this cultural carnage."

Hilgert, a key player in the effort to document endangered archaeological sites in Syria and Iraq, lamented the destruction in Palmyra.

"As a scholar, I mourn the ongoing obliteration of one of the most fascinating cities of the Ancient World, a symbol of cultural diversity and religious tolerance."

CNN's Ben Wedeman contributed to this report.