LONDON (AP) — A chess piece purchased for 5 pounds ($7.50) by an antiques dealer in Scotland in 1964 has been identified as one of the 900-year-old Lewis Chessmen, among the greatest artifacts of the Viking era.

Sotheby's auction house said Monday that the chess piece is expected to bring between 600,000 pounds ($670,000) and 1 million pounds ($1.26 million) at an auction next month.

The Lewis Chessmen are intricate, expressive chess pieces in the form of Norse warriors, carved from walrus ivory in the 12th century.

A hoard of 93 pieces was discovered in 1831 on Scotland's Isle of Lewis. It is now held in both the British Museum in London and the National Museum of Scotland in Edinburgh — but five of the chess pieces were missing.

The piece to be auctioned July 2, the equivalent of a rook, is the first of the missing pieces to be identified. It was passed down to the family of the antiques dealer, who did not realize its significance.

Sotheby's European sculpture expert Alexander Kader said the find is "one of the most exciting and personal rediscoveries to have been made during my career."