sentences:  It is uncertain when Roman concrete was developed, but it was clearly in widespread and customary use from about 150 BC; some scholars believe it was developed a century before that.Vitruvius, writing around 25 BC in his "Ten Books on Architecture", distinguished types of aggregate appropriate for the preparation of lime mortars.For structural mortars, he recommended pozzolana ("pulvis puteolanus" in Latin), the volcanic sand from the beds of Pozzuoli, which are brownish-yellow-gray in color in that area around Naples, and reddish-brown near Rome.