The Elgin (or Parthenon) Marbles are parts of the Parthenon and other monuments on the Acropolis in Athens, brought by Lord Elgin to London in the early 19th century.
Their provenance is not under dispute, but the matter of ownership is. The British Museum has a website that addresses, quick lucidly, their position on the Elgin Marbles.
I saw the Elgin Marbles this past week for only the second time in my life. And now having twice been to Athens, I am so glad that I spent time with these incredible pediment marbles and metopes on Thursday.
I also stared at the Rosetta Stone for a bit!