A Vietnamese mandarin cap believed to be from the Nguyen Dynasty has sold for 600,000 euros (693,243 USD) at a Balclis auction in Spain. (Photo courtesy of the Balclis auction house)

On the website of the Balclis auction house, the cap was described as "Vietnamese Mandarin cap from the Nguyen Dynasty, late 19th century-early 20th century." It comes with a box in lacquered and gilded wood, and has "some flaws and defects," the website said.

Tran Dinh Son, a researcher, said the cap belonged to a high-ranking mandarin, was well preserved and similar to artifacts on display in Hue, Ho Chi Minh City and Hanoi, meaning it was not all that rare.

Before 1945, several families either buried the caps with the deceased mandarins or kept them for worship.