Nimrud, which was shown being blown up in a jihadist video Saturday, was once the jewel of Assyria, home to a treasure considered one of the biggest archaeological finds of the 20th century.
The Islamic State group released a video in which militants equipped with sledgehammers and power tools break artefacts before rigging the site with large barrels of powder.
The subsequent footage shows a massive explosion and its aftermath, suggesting the ruins of Nimrud- which lie on the Tigris about 30 kilometres (18 miles) southeast of Mosul - were largely levelled.
Nimrud, founded in the 13th century BC, is one of the most famous archaeological sites in a country often described as the cradle of civilisation.
"Nimrud was the capital of Assyria, during the new Assyrian era," said Abdulamir Hamdani, an archaeologist from Stony Brook University in New York.
The city, which is on UNESCO's tentative list of world heritage sites, is the later Arab name given to a settlement which was originally called Kalhu.
The ancient city was first described in 1820 and plundered by Western explorers and officials over subsequent decades. It was also looted and damaged during the 2003 US invasion.
The "treasure of Nimrud", unearthed in 1988, is a collection of 613 precious stones, gold jewels and various ornaments which some archaeologists described as the most significant discovery since Tutankhamun's tomb in Egypt in 1923.
The treasure, which dates back to the Assyrian empire's heyday around 2,800 years ago, was briefly displayed at the National Museum in Baghdad before Iraq invaded Kuwait.
It was then hidden and its fate remained unknown until it was discovered in 2003, soon after US-led troops toppled Saddam Hussein's regime, in a bombed out central bank building.