Syria's cultural treasures are also conflict victims (AP) BEIRUT - On its towering hilltop perch, the Krak des Chevaliers, one of the world's best preserved Crusader castles, held off a siege by the Muslim warrior Saladin nearly 900 years ago. It was lauded by Lawrence of Arabia for its beauty and has been one of the crown jewels of Syria's tourism. But it has fallen victim to the chaos of Syria's uprising and the crackdown against it by President Bashar Assad's regime. Recently, gunmen broke into the castle, threw out the staff and began excavations to loot the site, says Bassam Jammous, general director of the Antiquities and Museum Department in Damascus. Syria's turmoil is threatening the country's rich archaeological heritage, experts warn. Some of the country's most significant sites have been caught in the crossfire in battles between regime forces and rebels. Others have been turned into military bases, raising archaeologists' fears of damage. Regime shelling of neighborhoods where the opposition is holed up has smashed historic mosques, churches and souks, or markets. Looters have stolen artifacts from excavations and museums. In one of the most egregious examples, shells thudded into the walls of the 12th century al-Madeeq Citadel, raising flames and columns of smoke as regime forces battled with rebels in March. The bombardment punched holes in the walls, according to online footage of the fighting. Local activists said regime forces carried out the assault and afterward moved tanks into the hilltop castle. Later footage showed bulldozers knocking through part of the walls to create an entrance. The government and opposition have traded blame for damage and looting of sites around the country. But a group of European and Syrian archaeologists tracking the threats through witness reports from the ground says that in several cases, government forces have directly hit historic sites and either participated in or turned a blind eye to looting. UN: Both sides in Syria are violating the truce Obama tightens penalties on Iran, Syria Syrian activists: Deadly shelling at farm village "We have facts showing that the government is acting directly against the country's historical heritage," said Rodrigo Martin, a Spanish archaeologist who has led past research missions inside Syria. What's happening is reminiscent of Iraq's chaos in the wake of Saddam Hussein's 2003 fall, when Baghdad's major museum was looted, and of Egypt, where looting has reportedly increased at archaeological sites around the country in the turmoil since longtime President Hosni Mubarak was toppled last year. An important crossroads, Syria's rich archaeological treasures extend over millennia. The capital, Damascus, is often claimed to be the oldest continuously inhabited city in the world. Archaeologists have uncovered cities dating back 5,000 years to the early Bronze Age, and the country is dotted with "tells," or hills, that likely hide more such cities, still not excavated. A series of cultures have left their mark - from Biblical civilizations, Alexander the Great's successors and the Romans to Christian Crusaders and Muslim kingdoms. "What we know of Syrian heritage has already provided a huge quantity of information, but we can safely say that the part that has not yet been studied is even bigger," said Martin. Each incident of destruction "is like burning a page in the book of history of mankind." The heritage also helped fuel tourism that was steadily rising before the crisis, giving a much-needed economic boost. More than 8.5 million tourists visited Syria in 2010, 40 percent more than the year before. Now there are virtually zero. The nearly 2,000-year-old ruins of Palmyra, an ancient oasis city that was one of the biggest tourist draws with towering Roman colonnades and a temple to the god Baal, stand deserted. Government forces have surrounded it and the nearby town and have set up a base in a historic castle on a hilltop overlooking the site, deep in Syria's central deserts.