The subject of this book is the dialogue between architect and foreman and its effect on Roman architecture. It was standard practice in Roman times for the architect's construction program to be taken over and given material form by the foreman and his workers, who adopted a distinctly operational process. This practice was also reversed, particularly in cases where construction requirements led to innovative technical solutions, with some special measures formulated on the ground being taken up and adopted by the architect, who would then make use of them in later projects. While the former practice has been the focus of much previous research, this study looks at the latter practice, which has been little examined. This study explores some specific cases that illustrate the dialogue from foreman to architect, presenting to the reader sites where the professionalism and skills of the workers made it possible to try out innovative solutions that could be developed independently. They could also be adapted for future projects, making the site a laboratory of constant experimentation.