Islamic State (ISIS/ISIL) militants have destroyed three ancient arches in the city of Palmyra, Syria, in the latest stage of their campaign to demolish important historic monuments across the territories of Iraq and Syria.

The UK-based Syrian Observatory for Human Rights said the jihadists used explosives to destroy the 2,000-year-old arches Sunday while leaving the supporting columns in place, apparently because the symbols and inscriptions on the arches clash with the radical Islamist ideology of the group.

ISIS holds the pre-Islamic monuments of the region to be idolatrous. Since seizing the city in May, ISIS extremists have destroyed the shrine of Baal Shamin and the Temple of Bel. The Temple of Bel was 2,000 years old and regarded as the greatest gem of Palmyra’s antiquities.

Along with ideological opposition to the monuments, ISIS is also funding its “Caliphate” by selling ancient artifacts on the black market, according to reports.

“We have received news from the site that the Arch of Triumph was destroyed [Sunday]. IS booby-trapped it several weeks ago,” said Syrian antiquities director Maamun Abdulkarim.

“This is a systematic destruction of the city. They want to raze it completely,” Abdulkarim told AFP, adding that the next archeological jewels risking demolition “are the amphitheater and the colonnade.”

Since May 20, 2015, the Islamic State has controlled Palmyra, a Roman-era oasis town in Homs province about 150 miles northeast of the Syrian capital of Damascus. Palmyra is known as the “Pearl of the Desert” and is listed as a World Heritage Site by UNESCO, the United Nations’ cultural arm. It contains important architecture combining Greco-Roman influence with Persian traditions.

Palmyra is situated near a hot-water spring called Afqa, which made it an ideal stopping point for caravans moving along the silk route between Iraq and Al-Sham. Its strategic location brought wealth to Palmyra beginning in second century BC.

Prior to Syria’s civil war, which began in 2011, Palmyra attracted 150 thousand tourists a year.

Follow Thomas D. Williams on Twitter @tdwilliamsrome.