A diamond necklace with a bow clasp, thought to have been commissioned by Catherine the Great (1729-1796), is to sell at Sotheby's.
The piece is one of two spectacular pieces of jewellery from the courts of the Russian Tsars to be offered in the Magnificent and Noble Jewels auction in Geneva on November 16.
It's valued at $3m-5m.
The piece dates to around 1760-1780 and was originally created as two separate jewels.
It was part of a collection of imperial treasures moved from St Petersburg to Moscow following the outbreak of the first world war.
After the revolution, the lot arrived in the UK - where it was sold in the 1927 auction of the Russian State Jewels.
A diamond parure that Catherine the Great may have given as a gift to the Ottoman sultan Ahmed III during peace negotiations during the Russo-Turkish war in 1711 is also valued at $3m-5m.
The gesture apparently worked and the Ottomans called off their campaign against the massively outnumbered Russians.
David Bennett, chairman of Sotheby's international jewellery division, said: "These two stunning jewels carry with them a fascinating insight into the luxury and opulence of the Russian court.
"It is difficult to overstate their rarity and historical importance..."