EDITOR's Note: Every week we look at a work of art or a cultural relic that puts the spotlight on China's heritage.

Rare guqin - traditional plucked seven-stringed zithers - dating back to ancient times have been selling like hot cakes at recent auctions in China.

A Song Dynasty (AD 960-1279) guqin sold for a record 136.64 million yuan ($20.77 million) at Beijing Poly's autumn auction in December, becoming the first Chinese instrument to fetch an auction price of more than 100 million yuan.

Since 2003, when a guqin named Remnants by the Mahatma (Da Sheng Yi Yin) from the Tang Dynasty (AD 618-907) sold for 8.91 million yuan ($1.34 million), the guqin, long viewed as an embodiment of Chinese music, philosophy and culture, has been attracting much attention in the Chinese auction market. It is estimated that there are only about 2,000 ancient guqin still in China.

"It is the vintage guqin's rarity that is one of the reasons for its growing popularity among collectors," says Zheng Minzhong, senior guqin expert with the Palace Museum in Beijing.

As per legend, the guqin was invented by the prehistoric figures Fuxi and Shennong, endowing it with a history spanning some 5,000 years.

Known as the "instrument of sages", it ranks as the first of a "scholar's four treasures" - the others being weiqi (Chinese Go), calligraphy and ink painting - and has been praised by many great names, such as Confucius (551-479 BC) and Song Dynasty emperor Huizong (1082-1135).

The guqin's round surface board is supposed to represent heaven and its flat bottom board, earth. As per Chinese measure, the standard length of a guqin is 3 chi, 6 cun and 5 fen (about 1.22 meters), representing the 365 days of a year.

The 13 dots on the surface, called hui, indicate the position of the harmonics. They stand for the 12 months of a year, plus a 13th month every two or three years as per the lunar calendar.

There are more than 50 shapes of the instrument. Some are named after the objects they resemble, such as jiaoye, or banana leaf, and lianzhu, or string of pearls. Some are named after their creators. For example, Zhongni refers to the style created by Confucius, and Shennong to the kind made by Shennong, the legendary figure.

The Da Sheng Yi Yin is an excellent example of the Shennong style.

Once in the collection of the Qing royal family, it's a masterpiece among the post-Tang guqin.

Made in 756 by Tang emperor Suzong, the Da Sheng Yi Yin is lacquered in black and chestnut-brown with 13 gold hui on its surface, and a carved name, seal and poem on its back.

The lacquer is covered throughout with several crack-like patterns called duanwen, which hold the key to determining a guqin's age.

"I believe the Da Sheng Yi Yin is typical of the mid-Tang period," says the Palace Museum's Zheng, who has written several papers and books on vintage guqins.

The uniqueness of a guqin is also reflected in its tablature, called jianzipu, which is specifically designed for every instrument, Zheng says.

This unique notation is a combination of written Chinese characters and numbers, each of which pack a load of information on such aspects as the position of the fingers and the plucking technique.

In 1977, a recording of the guqin piece Liu Shui, or Flowing Water, performed by master Guan Pinghu (1897-1967), was chosen to be included in the Voyager Golden Record, which was sent into outer space by the US-based National Aeronautics and Space Administration (NASA) on the Voyager 1 and Voyager 2 spacecraft.

In 2003, guqin music was made one of the Masterpieces of the Oral and Intangible Heritage of Humanity by UNESCO. It is now a popular instrument practiced by tens of thousands of professionals and amateurs across the country.