Digging out Dingling. [Photo by Zhang Wei/China Daily]

So they began digging. Two hours later, a stone stele was unearthed bearing the characters sui dao men, or tunnel gate. Ten days later, as the team arrived at 4.2 meters underground, they discovered brick walls on both sides of an 8-meter-wide path that ran along the circular wall of the Treasure City. In retrospect, the path, called "the brick tunnel" was the route the colossal coffins of the emperor and his two empresses traveled after their arrival at the mausoleum.

However, a promising beginning did not lead to a quick ending. After digging for months and finding nothing, the team jumped ahead and dug more along that same route, but still found nothing.

"It seemed that they had assiduously followed this clue that rolled out before them like thread from a skein, only to arrive at the end and find nothing but the end of the thread. It was in July and August, with rainwater constantly filling the trench. Yet just when most people were about to give up, the emperor, if you like, sent another beckoning."

The team unearthed a second stele. Inscribed on it was a line of words that translates as: "From here to the wall, the horizontal distance is 53.28 meters, and the vertical distance is 11.66 meters."