The Greeks and, especially, the Romans are famous for the heroic engineering of their aqueducts, tunnels and roads. They also measured the circumference of the earth and the heights of mountains with fair precision. This book presents new translations (from Greek, Latin, Arabic, Hebrew and Syriac) of all the ancient texts concerning surveying, including major sources hitherto untapped. It explores the history of surveying instruments, notably the Greek dioptra and the Roman libra, and with the help of tests with reconstructions explains how they were used in practice. This is a subject which has never been tackled before in anything like this depth. The Greeks emerge as the pioneers of instrumental surveying and, though their equipment and methods were simple by modern standards, they and the Romans can be credited with a level of technical sophistication which must count as one of the greatest achievements of the ancient world.