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NEW: ISIS captures Syrian border post, now controls all Syrian stations on border with Iraq

A Palmyra resident says ISIS fighters went door-to-door in conquered Syrian city

ISIS lauds fighters for "liberating" Palmyra and taking over a prison and military base

CNN  — 

“They are everywhere.”

That’s a 26-year-old Syrian’s stark observation about ISIS fighters in Palmyra, detailing the terrorist group’s swift, destructive takeover of yet another city in the brutal quest to expand its caliphate in the Middle East.

The capture of Syria’s ancient city threatens a UNESCO World Heritage Site described as having “stood at the crossroads of several civilizations,” with its art and architecture mixing Greek, Roman and Persian influences, according to that U.N. group.

U.N. and Syrian officials have expressed fears that ISIS will destroy the ruins, just as it flattened the ancient Assyrian city of Nimrud and smashed statues in Iraq’s Mosul Museum.

But Palmyra, also known as Tadmur, isn’t just a historical site. It’s home to tens of thousands of people, many of whom fear they’ll meet the same fate as others ISIS has conquered.

They’re people like the 26-year-old who asked to remain anonymous for fear of retribution. He’s huddled in a house with 50 others, including his family and neighbors who have lost their homes, and he’s worried food will run out while his city is under curfew.