We are surrounded by and sometimes still use structures dating from the middle ages. Scholarship has recreated its political, economic, social and military history. Specialists debate the finer details of medieval science, education and technology. The architecture of cathedrals, monasteries, churches and castles is painstakingly examined and re-examined and their functions are explored in both academic conferences and the popular media. But there are fewer studies of the people responsible for these works. And even fewer of military engineers – who may well have been involved in both the construction and the destruction of military fortifications.

I began to ponder this even while completing my History of the Early and Late Medieval Siege. The names of engineers at war kept appearing in contemporary accounts, increasingly as more records survived. Evidently, by the time of the renaissance in Europe, a body of expertise existed that rulers called upon to fulfil their engineering needs, and some of those experts’ names are well known today (if the number of exhibitions devoted to Leonardo da Vinci is any guide). It is also clear that engineering continued to be undertaken across the world even when there is no surviving record of it. But what had happened before?

I was at first anxious that it would not be possible to attempt this history because of a lack of evidence. Closer study suggested that, especially for the early centuries, it was necessary to offer rather more in the way of hypothesis than a historian ought to be happy with, and to read back from later reports into earlier times, something that also involved making unprovable assumptions. Nonetheless, there was sufficient to show that this king or that prince had successfully bridged a great river, or had built engines against a hostile fortress, or had laid out and defended a camp, or had diverted a river, and thus to identify that to have done so required having access to a degree of engineering skill that it was highly unlikely the rulers themselves possessed. That the necessary technical skills also existed can be confirmed from evidence in other fields: planning, layout and construction of buildings, hydraulic engineering (canals, dams, irrigation) or shipbuilding, all areas where archaeology has added immensely to knowledge of the past. Craftsmen built ships, houses or watermills with evident skill.