(FILES) A man walks in the ruins of ancient Persepolis, which served as the capital of the Achaemenid Persian Empire (550-330 BC), in southern Iran on May 13, 2024. Conservationists at Persepolis, Iran's most iconic ancient site, are waging a delicate battle against a tiny but persistent adversary: the lichen, a symbiotic organism that grows on surfaces like stone eroding millenia-old monuments, in a fight to preserve the integrity of the site's structures and its intricate carvings. (Photo by ATTA KENARE / AFP)