The collapsing amphitheatre at Fidenae symbolises the threat that Tiberian dissimulation poses to the future, a threat countered (and replicated) in the partial assimilation of past and present which makes history possible. Despite Tacitus' claim that historical memory is resistant to tyrannical repression, the struggle for control of the past in anticipation of an imagined future remains dominated by imperial power of permitted meanings. This struggle for control can be situated in Tacitus' text: the conflict between the senatorial tradition of history and the imperial politics it narrates. The dynastic history which we have already seen emerging in the figures of Germanicus and Agrippina threatens to overwhelm this tradition. Tacitus emphasises the construction of dynastic history in his narrative of the later Julio-Claudian emperors, Claudius and Nero. In particular the figure of Claudius, the historian turned emperor, can be read within the dynamic of a dynastic history which he first seeks to construct and by which he is later circumscribed, when narrative control is taken over by his second imperial wife, the younger Agrippina.