By Daniel Mansfield, Senior lecturer, UNSW This stone tablet records the restoration of certain lands by the Babylonian king Nabu-apla-iddina to a priest. Babylonian, circa 870 BCE. From Sippar (Tell Abu Habbah) Wikipedia Our modern understanding of trigonometry harks back to ancient Greek astronomers studying the movement of celestial bodies through the night sky. But in 2017, I showed the ancient Babylonians likely developed their own kind of “proto-trigonometry” more than 1,000 years before the Greeks. So why were the Babylonians interested in right-angled triangles? What did they use them for? I have spent the past few years trying to find out. My research, published today in Foundations of Science, shows the answer was hiding in plain sight.