Books VIII, IX, and X of De architectura form the basis of much of what is known about Roman technology, now augmented by archaeological studies of extant remains, such as the Pont du Gard in southern France. Numerous such massive structures occur across the former empire, a testament to the power of Roman engineering. Vitruvius's description of Roman aqueduct construction is short, but mentions key details especially for the way they were surveyed, and the careful choice of materials needed.