NIMRUD, Iraq -- When ISIS swept into Mosul two years ago, Leila Salih begged the militants not to destroy the Mosul Museum, where she worked, or at the archaeological site at Nimrud, which she helped oversee, just south of the city. "I told them we would destroy the graves ourselves if they just left the buildings standing," she told NBC News. "I begged them to save Iraq's history." But the pleas fell on deaf ears. Several videos released by the militants last year show ISIS fighters using sledgehammers, power tools, and bulldozers to demolish priceless sculptures and stone carvings. What they didn't destroy with explosives they tore down by hand. Built three thousand years ago -- and forgotten for centuries -- the ancient city of Nimrud was the second capital of the Assyrian empire, which at its height extended to modern-day Egypt, Turkey and Iran. Archaeologists first began excavating Nimrud in the 1840s, finding the remnants of ancient palaces, sculptures, and cuneiform tablets -- some of the earliest examples of writing known to man. The UNESCO heritage site was considered one of the most important archaeological finds in the world. Most famous for its colossal Lamassu sculptures -- hulking winged mythical beasts with a human face, the body of a bull and the wings of an eagle. The site was leveled by ISIS last year but retaken by Iraqi forces last month. Today, the ancient city lies in ruins. Salih tears up thinking about Nimrud's destruction -- 60 percent of what's been excavated now gone, according to her estimate. Seeing Nimrud as a schoolgirl inspired her to become an archaeologist; many of her colleagues are still trapped inside the city. "It is a tragic thing -- our culture, our history, our memories," she says, wiping her eyes. "They tried to destroy the identity of Iraq. The only thing we can do now is document the damage so we can start thinking of how to rebuild again." A recent visit to Nimrud revealed the devastating scale of the destruction. Just the archway entrance to famed Northwest Palace, built by the Assyrian King Ashurnasirpal II, remains, surrounded by piles of rubble. The fragments of its former winged guardians lie in a heap nearby. Although ISIS fighters have been pushed out, the site lies unprotected. Sheikh Khalid al-Jabbouri, a local tribal commander from Nimrud, says he wept when he first saw how little remained of the ancient city that generations of his family used to take care of. "I wasn't as devastated when they destroyed my house or when they killed some of my relatives because this is life -- all of us die," he says, surveying the damage. "But Nimrud was like a part of our family. This heritage was part of our lives, part of all of Iraq." Iraq has lost thousands of precious objects from its national museum and other