Among the significant archaeological sites endangered is the Temple of the Storm God, which dates from the third to the second millennium B.C. and which Ms. Burnham identified as one of the oldest structures in the world. Never opened to the public, the recently discovered temple and its huge carved reliefs are protected only by sandbags and a flimsy corrugated tin roof, she said.

Aleppo’s labyrinthine streets reveal a microcosm of human history. Beneath the Citadel are remains of Bronze Age friezes and Roman fortresses. The entire walled Old City, with its 12th-century Great Mosque, thousands of pastel-colored medieval courtyard houses, Arab souks and 17th-century stone madrasas, an Ottoman palace and hammams, is recognized as a World Heritage Site by Unesco, the United Nations cultural arm.

Images of the Citadel show rubble in some locations, but it is difficult to verify the extent to which either side is responsible for any damage.

The Syrian National Council, a coalition of antigovernment forces, issued a communiqué saying that the Citadel was damaged on Friday by an army rocket. Al Jazeera filmed rebels last week talking about the need to capture the Citadel.