The Great Wall is held together with sticky rice

Here is the Great Wall detail I love, and almost everyone misses it because they are too busy taking in the scale of the thing. Everyone knows it snakes over the mountains for thousands of miles. Hardly anyone asks the humble question underneath: what has actually been holding all that stone together for six hundred years? The answer turns out to be sticky rice.

When Ming dynasty builders wanted a mortar that would truly last, they boiled up glutinous rice, the same sticky rice you eat with dumplings, and mixed the milky soup into their slaked lime. In 2010 chemists at Zhejiang University finally explained why it works so well. A starch in the rice called amylopectin weaves through the lime as it hardens, keeping the mineral crystals small and tightly packed, so the finished mortar sets denser, tougher and much more water resistant than plain lime. The Ming stretches built this way have survived earthquakes, refused to let weeds through the joints, and in one case even resisted a bulldozer.

I painted the Wall in watercolour and ink, the pale towers riding the green ridges into the haze, and the whole time I kept thinking about those builders stirring pots of rice soup on the mountainside. There's a poster with a letter home and a postcard if you'd like one.

Shop the poster here:  The Great Wall, China · Travel Poster