The 18th-century Russian treasure was purchased by an anonymous telephone bidder for 10 times its presale estimate of $120,000, Sotheby's auction house said.

The estate of the original owner, George Roberts, learned of its importance during an appraisal over the summer. Roberts purchased it in 1951 from a London dealer.

Experts believe that as few as 10 of the bejeweled miniatures were bestowed by Peter the Great on his subjects for their exceptional service to him. Until the latest discovery, only five were known to exist, three of them in museum collections.

In 2001, one of the two in private hands sold for $132,500 at Christie's.

The 3 1/2-inch-high oval portrait sold Monday depicts Peter the Great in a blue cape and the sash of the Order of St. Andrew. The frame hangs from an imperial crown surrounded with diamonds. The reverse side is engraved with a triple-crowned, imperial double-headed eagle.

While believing it had some value because of the diamonds, Roberts' granddaughter, who lives in northern Arizona and did not want to be identified, had no idea it had historic importance, Sotheby's said. After her grandfather bought it, it spent some time in Illinois where he lived and finally ended up in Arizona where the family kept it in a display cabinet.

On the Net: www.sothebys.com

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AP-WS-11-02-09 1435EST