The Elgin Marbles are part of the Parthenon which were transferred to the the British Empire by Lord Elgin. Greece has been demanding them for quite some time now. The Wikipedia article says that Elgin took them in consent of the Ottoman Sultan which ruled then conquered Greece (The Greek war of independence happened in 1821 and Elgin transferred them to England between 1800-1810). But the monument itself wasn't Ottoman it is Ancient Greek so sure okay Elgin took them.
Shouldn't they be returned since the rightful owners (sovereign Greece) demand them back? What does the International law say for this type of situation?