The fortified plateau above Athens known as the Acropolis is the site of some of the most remarkable architecture in the world: its marble structures built in the fifth century BC, including the renowned Parthenon, represent the artistic peak of classical Greek architecture. NOVA examines how the heavily polluted air of Athens produces acid rain which is dissolving the marble sculptures and columns; and how iron tiles used extensively in repair 40 years ago are now rusting, expanding and shattering the stone structures.