druids, during which time they had to learn all the associated lore by heart. He also said that their main teaching was "the souls do not perish, but after death pass from one to another". They were concerned with "the stars and their movements, the size of the cosmos and the earth, the world of nature, and the power and might of the immortal gods", indicating they were involved with not only such common aspects of religion as theology and cosmology, but also astronomy. Caesar held that they were "administrators" during rituals of human sacrifice, for which criminals were usually used, and that the method was by burning in a wicker man. Though he had first-hand experience of Gaulish people, and therefore likely druids, Caesar's account has been widely criticized by modern historians as inaccurate. One issue raised by such historians as Fustel de Coulanges was that while Caesar described the druids as a significant power within Gaulish society, he did not mention them even once in his accounts of his Gaulish conquests. Nor did Aulus Hirtius, who continued Caesar's account of the Gallic Wars after Caesar's death. Hutton believed that Caesar had manipulated the idea of the druids so they would appear both civilized (being learned and pious) and barbaric (performing human sacrifice) to Roman readers, thereby representing both "a society worth including in the Roman Empire" and one that required civilizing with Roman rule and values, thus justifying his wars of conquest. Sean Dunham suggested that Caesar had simply taken the Roman religious functions of senators and applied them to the druids. Daphne Nash believed it "not unlikely" that he "greatly exaggerates" both the centralized system of druidic leadership and its connection to Britain. Other historians have accepted that Caesar's account might be more accurate. Norman J. DeWitt surmised that Caesar's description of the role of druids in Gaulish society may report an idealized tradition, based on the society of the 2nd century BC, before the pan-Gallic confederation led by the Arverni was smashed in 121 BC, followed by the invasions of Teutones and Cimbri, rather than on the demoralized and disunited Gaul of his own time. John Creighton has speculated that in Britain, the druidic social influence was already in decline by the mid-1st century BCE, in conflict with emergent new power structures embodied in paramount chieftains. Other scholars see the Roman conquest itself as the main