Substantial debate surrounds the relative lack of formal burials in Britain during the fifth century AD, which was a key period of social and economic transition following the withdrawal of the Roman army. Here, the authors argue that the ‘missing fifth century’ may be explained, in part, by the continuation of archaeologically invisible mortuary treatments practised in the preceding Iron Age and Roman period. Compilation of published radiocarbon dates from human remains found in cave and riverine contexts demonstrates that a variety of methods for the disposal of the dead—outside of formal cemeteries—existed in the first millennium AD.