These chess pieces are part of a collection discovered in Lewis in 1831, dating from the twelfth century and being made from walrus ivory. There were 78 chess pieces, so enough for multiple sets, and it’s unknown how they managed to end up on the Outer Hebrides. The best guess it seems is that they were lost during transport from Norway to Ireland, so someone probably managed to lose them over the side of a ship.
Of the 78 pieces, 67 were purchased by the British Museum and 10 were purchased by Charles Kirkpatrick Sharpe, a Scottish antiquary. He was able to find another bishop piece and these 11 pieces were purchased by Lord Londesborough and later sold by him to the Society of Antiquaries of Scotland. The Society donated them to Royal Scottish Museum and they’re now on display here. In total there were enough for four chess sets, with all of the other pieces still being on display in the British Museum in London.