By Dr. Frederique Darragon, Independent Researcher; Former Visiting Professor, Sichuan University, China

Earthquakes are still unpredictable and can still be deadly, even if today’s state-of-the-art technologies of flexible foundations, shock absorbers, shear walls, reinforced concrete, etc, allow for the construction of earthquake-resistant buildings and skyscrapers. The people of the past did not have such sophisticated contraptions. Nevertheless, many of them understood the basic principles of high productivity, resulting in earthquake-resistant constructions. It was not always the case: for example, the Peloponnese Mani inhabitants, who, because of their towers, repelled numerous invasions, did not figure out how to make their towers, which were rather modest in size, earthquake resistant until the 17th century.

But, nearly two millennia ago, many Himalayan illiterate tribes inhabiting the Sino-Tibetan Marches had created fiercely independent princedoms (some of which were queendoms as recorded in the Chinese Annals of the time) and invented a concept of interlocking stone pillars interspersed with unpegged beams to construct towering edifices that could resist the frequent earthquakes and high altitude climate. Depending on their location in their relative environment, these towers were built for different uses: look-out and sending smoke signal posts, defensive structures, and family status symbols. The tallest and most flamboyant ones were hard to subjugate trading posts on ancient trade routes.

Based on the 113 wood samples I sent for carbon dating, construction went on from the 4th to the 15th centuries. In their day, such towers must have been counted by the thousands. Apart from numerous ruins, nearly 100 towers are still standing tall, improbably gracing steep slopes and deep ravines of this trade and migration corridor with their timeless beauty and outstanding technical achievement. It appears that construction stopped around the 16th century, or maybe the new towers were of a lower quality, and none are still standing today.

Towers can be found in four regions that roughly correspond to ancient tribes’ territories: in Sichuan, there are the lands of the Qiang, the Minyag, and the Jiarong; in Tibet, such towers only exist in two small ancient kingdoms of the Southeast: Nyang-po and Kong-po
Given the remoteness of this corridor of impossible terrain, with many peaks towering over 6000 meters and deep valleys where the Mekong, the Salween, the Yangtze, and their affluents rage towards the lower lands, each princedom had a slightly different natural environment. Only locally available materials were used: timber, local mud or clay, and stones of various shapes, hardness, and quality.

This knowledge did not come out of nowhere: early on, people must have realized that buildings made of wood were little affected by earthquakes because of the wood’s flexibility.

As most of this region is south of the 30th parallel, the tree line is around 4,000 meters in altitude. Still, the winters are cold, and the trees grow slowly; consequently, building houses only of timber would have put too much pressure on the environment. Buildings made of stone were also longer-lasting and more adapted to the harsh, high-altitude climate. So, people would build their dwellings of uncut, nearly dry stone and add beams inside the masonry to add tensile force. Wooden beams are frequently used in adobe construction but very rarely in stone construction. As “Habitat” demonstrated, this technique is practically only used on both sides of the Himalayas.

On the southwestern side (India, Pakistan), it is generally called Kath-khuni. It consists of a relatively large number of beams alternating with rows of stones and mud.

The eastern side (Sino-Tibetan Marches) consists mainly of stones with some mud and inserted unpegged wooden beams; some of these beams are inside the walls, while others circle the outside of the walls. Both technologies prevent the walls from splitting open. This technique is still used in today’s traditional houses. I discovered only another group of stone buildings including reinforcing beams: the Meteora monasteries in Greece; it appears this style did not spread.

But another technology was needed to build very tall, free-standing earthquake-resistant towers: interlocking pillars. From the outside, these towers appear similar to ancient towers found in Afghanistan, Iran, or India, but they are not. These three last-mentioned groups of buildings are, in reality, round towers with external buttressing pillars.

As we have restored quite a few of them, we have discovered the specific construction technique of the Himalayan towers. They are not made of a circular wall with outside buttresses; in fact, they are concave polygons whose zigzagging walls are themselves uniquely composed of interlocking pillars woven together, leaning into and buttressing each other. There could be five to 13 pillars, but the towers with eight or 12 pillars have resisted the earthquakes better. The towers with a different number of pillars are all reduced to a small number of tiny ruins.

Such an architectural concept is not seen anywhere else. Worldwide, several pentagonal, hexagonal, and octagonal towers exist, but all are convex polygons.

The houses and towers all have tapered tops, making them more stable. This feature is common in many ancient constructions, as it also prevents the weight of the top from crushing the bottom stones. In tall towers, special care was given to the relative hardness of the stones used.

The openings were small and few, first because towers were eventually used for defense and second because large openings would have weakened the construction. The types of foundations are difficult to assess. The Minyag and Jiarong towers are often built over rocky soil but have a “solid” bottom part of 3 to 5 meters. In Tibet, the towers have doors at the ground level; one fallen tower was excavated and had 3-meter-deep foundations.

As said earlier, many efficient high-tech solutions exist today to build earthquake-resistant city buildings; however, such technologies are too expensive, unavailable, or poorly implemented in rural settings. Consequently, it is of utmost interest to document and record these vernacular architect-less building technologies and ensure that this traditional knowledge continues to be used. Such action can save lives, protect intangible heritage, and reinforce local people’s cultural self-esteem.

For more information see:
HABITAT: Vernacular Architecture for a Changing Climate, edited by Sandra Piesik and published by Thames & Hudson, USA, May 2024