Australian scientists have managed to crack the code of a mysterious 3,700-year-old Babylonian clay tablet, revealing a level of mathematical sophistication that pre-dates the ancient Greeks by a whopping 1,500 years.

This Babylonian tablet, known as Plimpton 322, is the world’s oldest—and most accurate—trigonometric table, according to research published this week in Historia Mathematica. The University of New South Wales Sydney researchers who cracked the code say the tablet was likely used by mathematical scribes to calculate angles when designing palaces, temples, step pyramids, and canals. This discovery shows that the ancient Babylonians—and not the Greeks—were the first to study trigonometry, the mathematical study of triangles.

Plimpton 322 was discovered in the early 1900s in southern Iraq by famed archaeologist Edgar Banks, who would go on to be the inspiration for Indiana Jones. Dated to between 1822 and 1762 BC, the tablet likely originated in the ancient Sumerian city of Larsa. Analysis of the tablet showed that the ancient Babylonians knew about the Pythagorian Theorem long before the rise of ancient Greece, but the tablet’s exact purpose remained a mystery.

One of the stronger theories was that it was a teaching aid for checking quadratic problems, but new research conducted by UNSW scientists Daniel Mansfield and Norman Wildberger now confirms the markings on the tablet as a trigonometry table.

After conducting a historiographical analysis of the tablet’s purported purpose, Mansfield and Wildberger took a closer look at the tablet and its inscriptions. Plimpton 322 features four columns and 15 rows of numbers written in the cuneiform script of the time. Importantly, this text is written in a base-60 numbering system, also known as a sexagesimal system (think of it like the minutes on an analog clock). Its 15 rows describe a sequence of 15 right-angle triangles, which are steadily decreasing in inclination. Also, the left-hand edge of the tablet is broken, meaning parts of Plimpton 322 are missing.