Hundred-ton marble slabs lie at the center of the pathways leading up to the palaces, particularly at the Hall of Supreme Harmony and the Hall of Preserving Harmony.

 

One of the most distinctive architectural features of the palace complex is the elaborate carvings of dragons and phoenixes on these massive marble slabs. The largest slab, measuring 16.8 meters long and 3 meters wide, is located in front of the Hall of Supreme Harmony.

 

 How were the marble slabs transported? According to research by Jiang Li from Tsinghua University, a 500-year-old Chinese record confirms that in 1557, a 123-ton stone was transported in 28 days from a quarry to the Forbidden City using a wooden sled. Additionally, another historical record from 1596 describes a debate among imperial officials regarding how to transport additional stones to the Forbidden City. Some officials argued that manpower and sleds were the safest method for moving such massive and valuable stones.

 

However, both Jiang Li from Tsinghua University and Howard Stone, an engineering professor at Princeton University, found these theories impractical. Their analysis showed that 16th-century Chinese carts could not support stones heavier than 96 tons. Other hypothetical methods, such as wooden rollers or planks, would have generated too much friction, making transportation difficult, especially given the uneven terrain. As a result, the researchers concluded that imperial laborers likely built an “artificial ice road” during the winter to transport the stone.

 

The 70-kilometer-long "ice road" stretched from the quarry to the Forbidden City, passing over several rivers. A team of approximately 50 men would pull the stone along this frozen pathway. To maintain the slippery surface, wells were dug every 500 meters along the route. Workers would fetch water from these wells and pour it onto the path, creating a fresh ice layer to lubricate the road. Wet ice drastically reduces friction, making it easier to slide heavy objects.

 

Using this method, the massive slabs could move at a speed of 0.29 km/h—just fast enough to ensure smooth transport before the ice dried up. The analysis also found that Beijing’s average temperature in January was cold enough to produce ice strong enough to support the immense weight of these stones.