The pyramid that has eight sides, not four

Here is the Giza detail I cannot stop thinking about, and it is not the one on the postcards. Everyone knows the Great Pyramid as the last of the seven ancient wonders still standing, a mountain of limestone you can pick out from space. Hardly anyone knows that it is not actually the shape it appears to be.

Each of the pyramid's four faces is very slightly hollowed, folded inward down the centre so gently that the whole thing really has eight sides rather than four. The dip is less than a metre across a base of well over two hundred, so for almost the entire year you would walk straight past it. Then, on the mornings of the spring and autumn equinox, the low sun throws one half of each face into shadow and leaves the other lit, and the crease down the middle suddenly appears, splitting every side in two. A British pilot named P. Groves photographed it from the air in 1940, though the great surveyor Flinders Petrie had already measured the hollow back in 1883, and nobody can say for certain whether the builders meant to do it.

I painted the pyramid in watercolour and ink, warm stone against a desert sky, and the whole time I kept thinking about the millions of people who have stood at its foot and never been told to come back at dawn on the equinox and watch four sides quietly become eight. There's a poster with a letter home and a postcard if you'd like one.

Shop the poster here: The Great Pyramid, Giza · Travel Poster