On Architecture is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus as a guide for building projects. The work is one of the most important sources of modern knowledge of Roman building methods as well as the planning and design of structures, both large (aqueducts, buildings, baths, harbours) and small (machines, measuring devices, instruments). He is also the prime source of the famous story of Archimedes and his bath-time discovery. (Summary from Wikipedia)