Greek schoolchildren have demonstrated at the Acropolis in Athens to demand that the UK returns marble sculptures taken by Lord Elgin 200 years ago.
Organisers plan similar protests in London and elsewhere
Wearing orange jackets bearing campaign logos, about 2,000 pupils formed a human chain around the monument.
The marbles are part of the Parthenon, a 2,500-year-old temple.
Greece has long campaigned for the marbles' return. But the British Museum says they are better off in London, safe from pollution damage in Athens.
Organisers said the marbles were Greece's pride and dignity. They said the symbol of Greek democracy had lain mutilated for two centuries.
Campaigners have collected 65,000 signatures and sent 900 letters of protest to the head of the British Museum in London.
The marbles were removed by British envoy Lord Elgin at the beginning of the 19th Century.
The Greek government has for years campaigned for their return, saying they were illegally removed.
The museum says it is not at liberty to give them back, and believes they are well looked after and available for millions of visitors to see in London.
It says the marbles are safe from Athens's pollution that has damaged those still there.
An organiser of Tuesday's protest said campaigners would soon stage a similar event at the British Museum.
Other cities which hold pieces of the temple to the goddess Athena include Paris, Vienna, Palermo and Munich, according to the Greek culture ministry.