The Great Wall of China is a 3,100 mile stretch of fortifications built to protect against invaders, monitor immigration, and control and tax trade, making it the largest toll booth known to man. The earliest of constructions that now form the wall were built with rammed earth, or soil mixed with lime and rammed into a temporary form, as early as the 3rd century AD.
The majority of the great wall that stands today was built during the Ming dynasty of the 14th-17th centuries. Most sections are built with huge clay bricks laid in sticky rice mortar on top of stone foundations, pictured below. Rammed earth still lies at the center of these two sided walls.
The sticky rice mortar is made of rice soup mixed with slaked lime. According to Chemist Bingjian Zhang, Ph.D., the mixture of inorganic calcium carbonate from lyme and organic amylopectin from rice forms a binding agent stronger and more water-resistant than regular lyme mortar. In South America, the Incas also used an organic additive to improve the strength of clay mortar in stone construction, including at Cuzco and Machu Picchu. See our blog posts on Incan Stonework to learn more.
Legend has it some innovative quarrymen made a road of ice during winter to transport foundation stones to the building site at the Add to dictionary pass in order to meet a deadline and save their heads.