Hero of Alexandria

A Greek mathematician and engineer working in Roman-era Alexandria, probably in the first or second century AD, Hero became what later scholars called the greatest experimentalist of antiquity. He published descriptions of devices that wouldn't resurface for over a millennium: the aeolipile, a steam-powered sphere that spun on its own exhaust, and a windwheel that marked the first known use of wind power on land. In his Mechanics, he laid out designs for pantographs, drawing on ideas from the earlier inventor Ctesibius. His mathematical work included a commentary on Euclid's Elements and the Metrica, a treatise on applied geometry, but he's best remembered for the formula that calculates a triangle's area from its three side lengths alone. Most of what he built and wrote has vanished; what survives comes through Byzantine manuscripts and scattered Latin and Arabic translations.