Our sources for the study of Hadrian’s Wall are threefold. First there are literary sources, then inscriptions, and finally archaeological evidence.
The literary sources for the Wall are very sparse, but include historians, such as the biographies of Hadrian and Severus within the Historia Augusta which mention the Wall and the Notitia Dignitatum, a list of late Roman military officials which includes a section entitled Per Lineam Valli. Post-Roman and early medieval writers, such as Gildas and Nennius, are contentious and confused, but Bede’s Ecclesiastical History of the English People includes what appears to be an eyewitness description of the Wall as it was in the 8th century and, as such, of some use.
Epigraphy, the study of inscriptions – principally, but not exclusively, on stone – is fortunately a much richer resource, given the Roman penchant for leaving records of their building activities. These can range from formal monumental inscriptions, such as those from Milecastles 38 and 42 recording construction under the governor A. Platorius Nepos, to the so-called centurial inscriptions, which the army used to mark the sections built by legionary centuries. These all help contribute to our understanding of the units involved in the construction and garrisoning of the Wall. A series of decorated cooking pans, inscribed with fort names and apparently ‘souvenirs’ from the Wall, also sheds some light on the western half of the Wall.
Archaeology is the third strand to the source material and it is the most diverse. It provides evidence for the form of structures and how they developed over time, thereby supplying relative chronologies for the Wall components and their phases. Study of the pottery and coins can also aid the establishment of an absolute chronology for the system, but they are at best crude indicators and nowhere near as useful as tree-ring dating (dendrochronology) although, given the nature of the Wall and its associated structures, not one that has until now had a large role to play. The artefacts recovered from excavation also supply insights to the material culture of the garrison of the Wall and the soldiers’ families.