 Decker further asserted that the advanced state of ancient irrigation practices "rebuts sizeable parts of the Watson thesis," since for example in Spain, archaeological work indicated that the Islamic irrigation system was developed from the existing Roman network, rather than replacing it.Decker agreed that "Muslims made an important contribution to world farming through the westward diffusion of some crops", but that the introduction of "agronomic techniques and materials" had been less widespread and less consistent than Watson had suggested.Furthermore, there is clear evidence that agricultural devices such as watermills and waterwheels, shadufs, norias, sakias, water screws and water pumps were widely known and applied in Greco-Roman agriculture long before the Muslim conquests.