Few people know of their existence but they are believed to have been in a remote, tranquil and picturesque valley in western China for more than 1,300 years.
Line carvings on a cliff at the eastern entrance to the Leba Valley of the Yushu Tibetan Prefecture, in Northwest China's Qinghai Province form a number of human figures. They include a lady dressed in typical royal garb from the Tang Dynasty (618-907), a man in typical ancient noble Tibetan attire and a buddha.
Also found were a few maids and bodhisattvas (beings who compassionately refrain from entering nirvana in order to save others).
The tall headwear worn by the male Tibetan on the cliff carvings "is a sign of the nobility in ancient Peking University.
Judging from the carving style seen in the photographs taken on site, Su - who is an expert in Tang Dynasty grotto art - dated the carvings to the mid-seventh century, when Buddhism was first introduced to Tibet and became prevalent during the reign of Songtsen Gampo.
Although no written record of the carvings has been discovered to date, local Tibetans believe that they were an authentic legacy left behind by Princess Wencheng of the Tang Dynasty, who married the then Tibetan King Songtsen Gampo in 641.
Historical records show that, after he established his rule over Tibet in the early 7th century, Songtsen Gampo began to seek closer ties with the Tang Dynasty.
Starting in 634, he dispatched envoys twice to the Tang capital Chang'an (today's in Shaanxi Province) to propose a marriage alliance.
Li Shimin, the second Tang emperor, finally agreed to let him marry Princess Wencheng.
Trek of princess bride
There is little in written historical records about how the princess trekked over 3,000 kilometres from Chang'an to the seemingly bleak Qinghai-Tibet Plateau.
But it is known that she took the route first west from Chang'an to Xining in today's Qinghai Province, and then turned south at the Sun-Moon Mountain, a demarcation between agricultural and pastoral areas.
Further south, the princess and her entourage had to cut through three vast, barren and arid deserts known as tala.
Legends hold that Songtsen Gampo came all the way from Lhasa to meet his fiancee at the Zhaling and E'ling lakes near the source of the Yellow River, north of Yushu.
They climbed over the Bayan Har Mountain Range, 5,200 metres above sea level, and crossed the Yangtze River in its upper reach known as Tongtian (leading to heaven) River - before they reached a lush valley.
Names for the valley differ in various writings about it, but local Tibetans call it Leba Valley.
Although the records are few, people could imagine how the princess felt when she saw the green valley with streams and thriving plants against an azure blue sky after months of travelling.
According to the legends, the princess was so overwhelmed by the scenery at Leba that she spent a month in the valley with her husband.
A pious Buddhist since childhood, Wencheng was said to be full of gratitude to the Buddha for her arduous but safe journey, and she had the figures carved on the cliff by the Tongtian River.
The line carvings, done with vivid strokes, impress Su Bai and several other experts of ancient sculpture as "good work."
Wen Yusheng - emeritus curator of Longmen Grotto in Luoyang, Henan Province, and expert on Buddhist sculpture of the Tang Dynasty - said: "Obviously, it is a picture of worship of the Buddha."
Pointing to the figure of the Buddha, which is over three metres high, Wen said: "We can be certain that the figure is the Buddha because it not only has a halo around its head but also has a halo around its body. In Buddhism, only the Buddha is entitled to a body halo."
The man and woman in the carvings are both facing the Buddha. They are each half the Buddha's height and are each holding something in their hands.
The man is carrying a bowl-like container with a lid, while the woman has a flower, which Su said "should be a lotus."
Although the carvings have been exposed to the elements and eroded for more than 13 centuries, the lines are still distinct enough to the two worshippers' devotion in their facial expressions.
The Buddha looks calm and graceful, and the lines are distinct enough to show a gauze cloak draped over his body.
Simple as they might appear, the carvings provide rich information on the living standards and artistic attainment in those ancient times, Wen said. "They are very precious," the professor added.
Ancient connection
Lacking many written records, Su and Wen could not be sure whether or not the two worshippers are Songtsen Gampo and Princess Wencheng.
But the carvings are rare works of art from that period testifying to the ancient union of Tang and Tibet, they said.
Local Tibetans would insist that the two figures are the ancient Tibetan king and the Tang princess.
Deyang, a 10-year-old fourth-grade pupil in Jiegu, the seat of Yushu Prefecture, has taken several groups of visitors to the site. He tells them that, in the carvings, "Princess Wencheng and King Songtsen Gampo are worshipping the Buddha together."
Some 20 kilometres away, at the western entrance of Leba Valley, is a small but famous temple named after Princess Wencheng. Walking out of the valley 1,360 years ago, the princess reached the Batang Grassland before entering Tibet proper via Changdu.
Local Tibetans and the princess were reluctant to bid farewell to each other.
Qiuying Lanze, a Tibetan official with the Yushu prefecture government, said: "Princess Wencheng was said to have brought some cereal seeds and passed on the techniques to grow vegetables and mill flour here in the valley.
"It is also said that her footprints were carved on the cliffs there and people would come to worship them."
Along the valley are rocks carrying inscriptions of Buddhist canons in the Tibetan language.
"They are much more modern than the figure carvings, done in later days by pilgrims to show their respect for Princess Wencheng and King Songtsen Gampo," explained Qiuying Lanze.
Seventy years after Wencheng married Songtsen Gampo and 30 years after she died in Lhasa, Jincheng - another Tang princess - renewed the Tang-Tibet union by marrying another king of Tibet in 710 at his request.
Princess Jincheng took the same route as her predecessor.
It is said that the Princess Wencheng Temple was built at Jincheng's order.
What is unique about the temple is another set of inscriptions carved on cliffs behind the building. Inscribed on them is a Buddhist scripture in both Chinese and ancient Tibetan, with not many characters remaining discernible today.
"It's a pity that little research has been conducted into the Leba carvings and the inscriptions at Princess Wencheng Temple due to the lack of written records," said Li Zhixin, curator of the Qinghai Museum.
Li had a replica of the Leba carvings made, which is now on display in the museum in Xining, the capital of Qinghai Province.
(China Daily March 5, 2002)
