On the other hand, the rediscovery in recent years of plastic form has brought about a closer relationship between architects and engineers. In the wake of the phenomenon that is the work of Santiago Calatrava, figures of engineer-architects have emerged such as Cecil Balmond, Sasaki and Guy Nordenson, who have been able to give a strongly "engineering-oriented" guise to ever more complex building sites. To this we must add the rise of new issues, such as that of environmental engineering, which has changed from being a specifically technical sphere to one of many other realms of knowledge, not least the aesthetic. If, therefore, there is a phenomenon today that is able to hold together the various expressions of contemporary architecture, it is precisely this return to the structure and methods with which it is realized.