Far from being a compilation of readily available sources or a pastiche of previously published histories, this volume is the product of extensive primary research. The author has brought numerous documents to light for the first time, uncovering them from centuries of dusty neglect in libraries throughout Europe, and these manuscripts are the foundation of Gille's reconstruction of Renaissance technology. Even so, the existing documentation of this facet of Renaissance life is rather scanty compared with that concerning for example, the arts and commerce of the time. The reason appears to be that engineers pf the twentieth – were more inventive than articulate. If they left behind any written record at all, it was likely to be a sheaf of haphazard and rough notes. Gille observes that we tend to credit the few exceptions to this rule with more inventiveness than they possessed and to ignore their unlettered forerunners and colleagues, and he here begins the historical task of correcting the balance.

The author emphasizes the close continuity of technical invention from antiquity (in particular, the Alexandrian Greeks), through the mediaeval period (in particular,, the Germans), to its brief but brilliant high flaring among the Italians of the fifteenth century. The engineer of this age of action was well suited to his times: '... an artist and artisan, a military man, an organizer of festivities, a man of such complexity and genius that that it seemed that no effect was beyond his power.' The engineers were conscious of embodying the Archimedean tradition, the tradition of 'give me a place to stand and I can move the world.' It was an age marked by a close and natural mutuality between the technical and the fine arts, and by the first real union of science and technology, whose issue was a permanent enrichment of both. Science gave to engineering a new sophistication of mathematical precision, and the working models constructed for mechanical inventions prepared the way for a truly experimental science, as later developed by the generation of Galileo.

As might be expected, the figure of Leonardo da Vinci looms large in this book. It is the author's contention, based on the documents he has uncovered, that Leonardo's originality as an engineer has been greatly overestimated, that in fact he borrowed and adapted freely from the work of his anonymous and little0known contemporaries, that many of his ideas are already prefigured in the mediaeval period. Nevertheless, although he rests on the foothills leading up to him, he still towers above them as the consummate technical artist. After reading this book, one sees his genius in a more exact (and foreshortened) perspective, but one still cannot explain it: it retains its awe-inspiring proportions.