The conventional historic account maintains that international criminal law (ICL) was ‘born’ after the Second World War. This account is incomplete, as William Schabas's book, The Trial of the Kaiser (2018), captivatingly shows by richly portraying the (aborted) First World War initiative to try the German Kaiser before an international tribunal. However, this article (after providing an overview of Schabas's book) argues that Schabas's account of a First World War ICL ‘birth’ is also incomplete. ICL during the First World War era was but one link in a much longer historical chain. The essay demonstrates this fact by presenting certain elements of the long (forgotten) history of ICL, which provide answers to questions that have been left unanswered, not only by the conventional account (of a Second World War ICL ‘birth’) but also by Schabas's account (of a First World War ICL ‘birth’). As the article discusses, the unveiling of a greater ICL history indicates that international criminal tribunals are not a modern innovation, and reveals the origins of ‘crimes against humanity’, of ‘aggression’ and of the universal jurisdiction doctrine. The essay further discusses reasons for the non-remembrance of the long history of ICL, the importance of acknowledging that history, and the likelihood of it becoming widely acknowledged in the near future.