Viking-era artefact missing for almost 200 years to be sold next month after decades tucked away in Scottish home.

An eight-centimetre-tall wonder of the medieval world – purchased for a few dollars five decades ago and hidden in a household drawer for years – has been identified as one of the long-lost Lewis Chessmen and is now expected to fetch more than $1m at an auction next month.

The intricate Warder piece, one of a set of 93 found on Scotland’s remote Hebridean island of Lewis in 1831, is to be auctioned on July 2 at Sotheby’s auction house in London. On Monday, Sotheby’s confirmed its authenticity and said it was likely to fetch between $670,000 and $1.26m.

It is the first of five missing pieces from a Viking-era hoard, which comprised four chess sets with the exception of one Knight and four Warders, to be identified. Three Warders – the equivalent of a rook on a modern chess board – and the Knight remain missing.

The Lewis Chessmen are intricate, expressive artefacts in the form of Norse warriors, believed to have been carved sometime in the late 12th or early 13th century in Norway.

The discovery was announced after a family from the Scottish city of Edinburgh, who asked to remain anonymous, took the piece to Sotheby’s for an assessment.

The family’s late grandfather, an antique dealer, acquired the walrus ivory item from another seller for $6 in 1964. He catalogued it as an “Antique Walrus Tusk Warrior Chessman”, a spokesperson for the family said in a statement on Monday.

“From this description, it can be assumed that he was unaware he had purchased an important historic artefact,” the spokesperson added.

The Warder piece is expected to fetch between $670,000 and $1.26m at auction, according to Sotheby’s [Sotheby’s handout]

The piece was later passed down to the spokesperson’s mother, who tucked it away in a drawer in her home.

“From time to time, she would remove the chess piece from the drawer in order to appreciate its uniqueness … She believed that it was special and thought perhaps it could even have had some magical significance,” the spokesperson said.

‘Symbol of European civilisation’

According to Sotheby’s, the pieces were likely produced in Trondheim, the seat of the archbishop of Norway at the time. Until 1266 and the Treaty of Perth – which ended a military feud between Magnus VI of Norway and Alexander III of Scotland and granted Scotland control over the Hebrides – the Isle of Lewis was under Norwegian authority.

The items are widely believed to have been the stock of a trader, who may have buried them following a shipwreck. That theory is supported by the apparent lack of wear on the pieces.

The British Museum in London now holds 82 of the artefacts, while the National Museum of Scotland in Edinburgh has possession of 11. The latter has argued the chessmen should be permanently returned to Scotland.

Alexander Kader, a Sotheby’s expert who examined the newly discovered part of the set, described the find as “one of the most exciting and personal rediscoveries to have been made during my career”.

“Today all the chessmen are a pale ivory colour, but the new Lewis Warder’s dark tone clearly has the potential to offer valuable and fresh insight into how other Lewis chessmen may have looked in the past,” Kader said in a statement.

“There is certainly more to the story of this Warder still to be told, about his life over the last 188 years since he was separated from his fellow chessmen, and just as interesting, about the next chapter in his journey now that he has been rediscovered.”

Seen as an “important symbol of European civilisation”, according to Sotheby’s, the chessmen were included by Neil MacGregor, a former director of the British Museum, in his A History of the World in 100 Objects BBC radio series.

Describing the significance of the artefacts, MacGregor said: “Between them, these much-loved pieces take us into the heart of the medieval world.”