The Self-Propelling Stone of Ancient Tomb Mechanisms

In imperial tombs, anti-theft designs are rigorous, especially in the rear chamber (where the Xuan Palace is located). Along the long tomb passage dedicated to the movement of the coffin, there are generally at least three stone doors from the entrance to the underground palace, and up to seven in some cases. Each door has mechanisms, weighing several tons to dozens of tons, making them as solid as a fortress. The outermost layer is commonly known as the "Vajra Wall," and its location is quite concealed, making it difficult to find without insider knowledge.

The first imperial tomb excavated after 1949 was the "Dingling" of Emperor Shenzong of Ming, Zhu Yijun. This is also the only imperial tomb actively excavated by archaeologists to date. On May 19, 1956, archaeologists dug the first shovel of soil, but it wasn't until September 2 of that year that they found the legendary "Guide Stone" inscribed with "This stone is sixteen zhang from the front of the Vajra Wall, three zhang deep," which led them to the Vajra Wall.

Behind the stone door of the Vajra Wall stands another mysterious "Self-Propelling Stone." This stone is actually a rectangular stone pillar that acts as a door prop, having the miraculous effect of "one stone guarding the pass, ten thousand men cannot open it." The two stone doors of Dingling are extremely heavy, tall, and well-crafted, measuring 3.3 meters high and 1.7 meters wide; the self-propelling stone used to prop the door is 1.6 meters long, with remaining ink marks: "The self-propelling stones of the seven doors in the Xuan Palace have not been verified." What does this mean? Experts have not fully understood it to this day.

After the coffin is placed and personnel withdraw, leaving no one inside, how does the self-propelling stone prop the door? The secret lies in the design of the stone doors and their hinges. The edges where the two doors meet have interlocking grooves, and the upper and lower ends of the hinges are polished into spherical shapes. Additionally, at the same position in the middle of the two stone doors where the seam aligns, a protruding groove was left during carving. Before closing the stone door, craftsmen placed the self-propelling stone in a stone groove on the ground and used a special "7"-shaped tool, commonly known as a crooked nail, to hook the self-propelling stone. After all personnel had withdrawn from the underground palace, one door was closed first. The craftsmen pulled the crooked nail, causing it to tilt forward slowly, aligning with the reserved groove on the stone door. As the stone bar tilted, its immense weight would press against the hinged stone door, causing it to rotate. At this moment, the craftsmen quickly removed the crooked nail, and the stone door closed automatically until it was completely sealed. The self-propelling stone, inserted into stone grooves at both ends, would firmly prop the stone door shut, making it impossible for anyone unaware of the trick to open it.

The special object commonly known as the crooked nail functions similarly to a key. This "opening" method was mastered by thieves who entered houses for theft in ancient times, allowing them to easily open tied doors from the outside. Tomb builders and archaeologists actually borrowed this theft technique.

After thieves opened the first stone door, they might not necessarily find the second door. Tombs generally have multiple maze-like passages, and if one is not careful, they could get lost in a maze and be unable to get out. Finding the second stone door does not guarantee opening the third, as the "mechanisms" behind each stone door are not identical.

In 1928, warlord Sun Dianying looted the Eastern Qing Tombs, dividing his forces into several routes. When looting the tomb of Empress Dowager Cixi, the last stone door leading into the underground palace blocked him, and he could not open it for a time. He originally planned to use explosives to blast it open but feared damaging the treasures inside, so he resorted to a crude method: ramming. Forty soldiers used thick wooden poles to forcibly ram the stone door open, allowing them to enter. Investigators later found on-site that the self-propelling stone propping the door had been broken into several pieces.

Another group of soldiers encountered a bizarre incident while looting the Yuling of Emperor Qianlong. No matter how hard they tried, they could not open the stone door in front of the Xuan Palace, nor could they prop it open. Yuling houses the remains of Emperor Qianlong and Empress Xiaoxianchun, Noble Consort Zhe Min, and four others. After Qianlong's heavy coffin was placed on the stone bed in the underground palace, four heavy Longshan stones were placed at the four corners of the coffin to determine the fengshui line and calibrate the most prosperous direction of the dragon vein. The last stone door became a stumbling block. In desperation, they had to blast it open. After the stone door was blown open, the soldiers were surprised to discover a huge anomaly: the other five coffins were on the stone bed, but Qianlong's coffin had "walked" down and become the "self-propelling stone," firmly propping the stone door shut, preventing the soldiers from opening it.

Superstitious accounts suggest that Qianlong, knowing from the underworld that thieves would come to loot Yuling, came down personally to prop the door. However, a similar anomaly occurred in 1975 when archaeologists cleared the Yuling underground palace; Qianlong's coffin "walked" down to prop the door again. Some experts believe this was due to the buoyancy of groundwater seeping in, lifting the coffin. But why did the other five remain still? Moreover, the four corners of Qianlong's coffin were fixed with heavy stones. If it were due to groundwater buoyancy, significant waves would be required, which the seeping water obviously did not provide. The matter of Qianlong's coffin propping the door remains an interesting puzzle for which experts have not yet produced a convincing archaeological conclusion.

The self-propelling stone was a common method for sealing doors in Ming and Qing imperial tombs. Others used the "lever principle" for anti-theft door propping designs, which were common during the Qin and Han dynasties. Stone bars placed behind the door would automatically翘 up to prop the door shut, making it impossible to push open from the outside. To open it smoothly, one had to find a way to flatten the stone bar. In 1968, when archaeologists opened the tomb chamber door of Liu Sheng, Prince Jing of Zhongshan of the Han Dynasty, they discovered this anti-theft design.