Persepolis, one of the world’s largest archaeological sites, is under threat of serious damage from tiny lichens. Red and yellowish traces left by the half-algae, half-fungus organism are visible on the ruins, particularly on the immense pillars of the ancient Achaemenid city. “If we do nothing, these organisms could turn these relics into dust within 50 to 100 years”explains Shahram Rahbar, a curator of the site.
Listed as a UNESCO World Heritage Site since 1979, the city of Persepolis is one of the most visited sites in the country with 140,000 visitors in 2023. The ancient Achaemenid city was built in 518 BC by Darius I on a half-natural, half-artificial terrace in the middle of the desert 50 kilometers from the city of Shiraz, in the south of the country. A gigantic 13-hectare palace complex inspired by Mesopotamian models was erected by the Achaemenid kings.
The palace contains exceptional sculpted wall friezes and monumental gates called “propylaea” topped with winged androcephalic bulls. “It is an open-air museum reflecting twenty-five centuries of life in the Middle East. It is the foundation of Iran’s history, culture and socio-cultural life.”notes Alireza Asgari Chaverdi, the site director. There are also colossal sculptures and carved stone reliefs like the Archers frieze (from the time of King Darius I) in polychrome ceramic preserved in the department of oriental antiquities of the Louvre Museum.
The Throne Room, Palace of the Hundred Columns, Persepolis.
The sculpted wall friezes of the palace were particularly damaged by lichens: the parasitic organism took up residence in rock surfaces larger than 1.5 cm and gradually dissolved the minerals.
Other sites such as that of Bisotun, also listed as a UNESCO world heritage site, were affected in the province of Kermanshah. A sculpted inscription recounting the conquests of King Darius I has been largely damaged by lichens.
On site, teams of scientists use lasers and antibiotic-like substances to eliminate lichens. The proliferation of lichen is due to global warming: air pollution produces much more nitrogen, a real fertilizer for lichen, scientists explain. There are 300 species of lichen in Iran, of which 500 to 700 varieties currently proliferate on historic monuments. Acid rain and the harsh desert climate accentuate the phenomenon according to lichenologist Mohammad Shorabi.
The Persepolis site in Iran.
