A fortress for the whole clan
The Fujian Tulou are massive, multi-story rural dwellings built by the Hakka and Minnan people between the 12th and 20th centuries. These structures, whose name translates to "earthen building," are primarily found in the mountainous regions of southeastern Fujian. Built as self-contained worlds, a single tulou could house an entire clan of up to 800 people. The design is inward-facing, with a large central courtyard and a single, heavily fortified entrance. The imposing outer walls, which can be up to three meters thick at the base, are constructed from rammed earth mixed with local materials like sand and lime. Some builders even incorporated sticky rice and brown sugar into the mixture to improve adhesion.
The primary function of this design was defense against armed bandits who were common in southern China for centuries. The lower sections of the walls, sometimes reinforced with granite blocks, were immune to arrows and early gunfire. Windows were absent on the first floor and only appeared on the upper levels, which also featured gun holes for defense. The main gate was a formidable barrier, constructed from 10 to 13 centimeters of wooden planks reinforced with an outer iron plate. This construction made each tulou a self-sufficient fortress, enclosing halls, storehouses, wells, and living quarters within its protective walls.
Engineering an earthquake-resistant community
The materials science behind the tulou walls is important of their longevity. The main component is rammed earth, a composite material made by compacting a damp mixture of soil, sand, gravel, and clay. To increase the tensile strength of the walls, builders embedded bamboo strips and small wood pieces, which function similarly to rebar in modern concrete. This composite structure sits on a high stone foundation that prevents moisture from wicking up into the earthen walls.
This construction method gives the tulou remarkable seismic resistance. The thick, flexible rammed earth walls are effective at absorbing and dissipating the energy from an earthquake. Structural analysis shows that the circular shape is particularly effective, as it prevents the formation of weak points and distributes stress evenly throughout the structure, preventing localized out-of-plane failures. One famous example, the Huanji Tulou, built in 1693, reportedly survived a magnitude 7.0 earthquake in 1918. While the quake opened a 20-centimeter-wide crack in the wall, the building remained standing and the crack reportedly fused back together on its own. Inside, a wooden frame structure supports the floors and creates the individual rooms, but it is the massive earthen wall that provides the primary structural integrity.