This text breaks with the widely accepted research assumption that marriages in antiquity could only exist between women and men by examining whether marriages between same-sex partners existed in the Roman Empire. Using several documented cases and source passages, some of which have not yet been considered in research, it is shown that people could intentionally change their social gender status with the consent of their contemporaries and could marry a person of the same biological gender as part of their newly acquired gender-specific privileges. In connection with this, the classification of the phenomenon by contemporary authors, who were at least partially familiar with this practice and who also criticized it extensively, is also traced. Why these forms of gender fluidity and same-sex marriages existed and were tolerated at first despite criticism but were then criminalized in late antiquity and thus could not survive antiquity as a phenomenon, will be discussed in conclusion.