 A crucial factor in this development, which saw a trend toward monumental architecture, was the invention of Roman concrete ("opus caementicium"), which led to the liberation of shapes from the dictates of the traditional materials of stone and brick.These enabled the building of the many aqueducts throughout the empire, such as the Aqueduct of Segovia, the Pont du Gard, and the eleven aqueducts of Rome.The same concepts produced numerous bridges, some of which are still in daily use, for example the Puente Romano at Mérida in Spain, and the Pont Julien and the bridge at Vaison-la-Romaine, both in Provence, France.