jihadists shown smashing shrines and statues in 2,000-year old city that was declared a world heritage site in 1987 .
isis thugs recorded on ladders using hammers and ak-47s to smash down historic relics on the ancient walls .
the fanatics claim relics are ` false idols ' which promote idolatry that violate their interpretation of islamic law .
authorities also believe they have been sold on the black market by the terrorist group to fund their atrocities .