In the study of the structural elements of the Antonine Wall two scholars have made an outstanding contribution. The first, naturally, is Sir George Macdonald, who reduced the vast body of heterogeneous evidence to a semblance of order and put forward the earliest formal theories about the nature of the Wall and how it came to be built. For several decades thereafter the attention of scholars was concentrated upon the practical problems of individual sites along the barrier rather than the theoretical questions of origin and relationship. But it has never been appropriate to study any example of Roman military work in isolation, and it was not surprising, therefore, that the research activity on Hadrian's Wall in the years following World War II should have generated a spirit of enquiry about related problems on the more northerly frontier. In particular, it began to be asked whether the Antonine barrier might not be more closely comparable with Hadrian's Wall than had previously been suspected. Was it, for example, provided with structures corresponding to milecastles and turrets? Macdonald had already described the rare instances of minor works and enclosures, but these seemed too few in number and too irregularly disposed to fit the bill for either category. Excavation and aerial survey were soon to demonstrate, however, that fortlets bearing a close resemblance to Hadrianic milecastles had indeed formed an integral part of the defence-system. At Duntocher, Dr Anne Robertson showed that a fortlet had originally stood in isolation, some time before the curtain of the Wall itself was constructed, to be accompanied, in time, by a small secondary fort; Wilderness Plantation, on the other hand, was found to be bonded with the curtain and therefore exactly contemporary with its earliest stage. Although it was still widely argued that these minor works had been used solely to guard the longer intervals between Wall forts proper, it was not until John Gillam had presented what is rightly called ‘a seminal discussion paper’ that the hunt began in earnest for an extended series of ‘milecastles’ along the entire Antonine Wall. Like Macdonald forty years earlier, Gillam gave new impetus to mural studies; with what success several recent publications amply testify.