The primary evidence for Julius and Aaron comes from the writings of Gildas, who was writing somewhere in western Britain during the early to mid sixth century. There remains a question as to how the events that likely took place in third-century Caerleon were transmitted to Gildas, writing three centuries later. There is also the question as to how accurate his information about the events of the Romano-British past was; some of his claims, such as that Hadrian's Wall was built by Septimius Severus, were incorrect. Jeremy K. Knight believed that Gildas' information on Julius and Aaron should be taken seriously, for he was "a muddled, but honest, witness" to the information he received.