‘Lability’ and ‘labile verbs’ refer to the phenomenon of valency alternation without a formal change in the verb. In most cases, it concerns the alternation between transitive and intransitive constructions. That can be split up into P-lability (patient-preserving lability) and A-lability (agent-preserving lability). This project aims to conduct corpus-based research on the diachrony of Latin P-labile verbs. Little is known about the mechanisms behind the emergence of P-lability in Latin. First, we aim to define how P-lability fits within the diathetic system of Latin. Secondly, this project aims to reveal the semantic factors (Aktionsart, verbal classes, causalness degree) underlying the increase of P-lability in Latin. Furthermore, we will test the hypothesis of whether the change in morphosyntactic alignment played a role in the development of P-lability in Latin. Lastly, this project aims to describe the different pathways that P-lability followed in its development to the Romance languages. Consequently, research on P-lability in Latin will lead to a more profound understanding of the diachrony of P-lability as a diathetic category in general. Different Latin corpora covering as many periods, registers, and regions as possible will be used to investigate the diachronic, diatopic, and diaphasic variation of the syntax and semantics of labile verbs.