Hydraulics is a branch of science and engineering concerned with the mechanical properties of liquids. It is part of the more general discipline of fluid power. The word "hydraulics" comes from the Greek word ὑδϱαυλικός (hydraulikos) which in turn comes from ὕδϱαυλος meaning water organ which in turn comes from ὕδωϱ (water) and αὐλός (pipe). The earliest masters of this art were Hero of Alexandria and Ctesibius. The ancient engineers however focused on sacral and novelty uses of hydraulics, rather than practical applications. One of the founders of modern hydraulics was Benedetto Castelli, a student of Galileo Galilei.