As evidence, Artmann cites an "an ancient note written in the margins of
the manuscript" of Book XIII of Euclid's *Elements*:

*The Sophist*. Theatetus
seems to have worked on solid geometry between 380 and 370 BC, perhaps
inspired by Plato's interest in the subject.

You may know Theaetetus through Plato's dialog of the same name, where he's described as a mathematical genius. He's also mentioned in Plato's[This book is about] the five so-called Platonic figures which, however, do not belong to Plato, three of the five being due to the Pythagoreans, namely the cube, the pyramid, and the dodecahedron, while the octahedron and the icosahedron are due to Theaetetus.

He died from battle wounds and dysentery in 369.

Reference to:

- Benno Artmann,
About the cover: the mathematical conquest of the third dimension,
*Bulletin of the AMS*,**43**(2006), 231-235.