The year 2016 will be marked as a year in which identity politics reached new levels of significance. Among numerous dramatic events, the UK referendum on membership of the European Union has brought many issues of interest to archaeologists to the fore. These range from entirely contemporary concerns, such as the future of research funding in Britain, to topics of more longitudinal significance, including the interactions between different identity groups in particular economic and political circumstances. In this paper, I wish to explore aspects of the distinctive position of Britain as an illustration of identity dynamics in the long term, focussing on the relationship between imperialism and identities and viewed through the lens of recent work in Border Studies. Brexit can be seen as the culmination of the collapse of the British empire, and transformation of British identity, in the post-Second World War era and the particular dynamics of this process invite comparison with Britain’s earlier position as one of the frontier provinces of the Roman empire, especially in the 4th and 5th centuries AD. This comparison reveals two paradoxical dimensions of imperial identities, the first being that so-called ‘peripheries’ can be more important than ‘cores’ in the creation of imperial identities and the second that such identities can be simultaneously ideologically powerful yet practically fragile in the circumstances which follow imperial collapse. Such insights are important because, at a time of apparently resurgent nationalism in many countries, archaeologists need to work harder than ever to understand identity dynamics with the benefit of time depth.