This chapter explores the competition between the use of the dative case and the prepositional construction featuring ad ‘to’ to encode the third argument of ditransitive verbs in Merovingian Latin. Unlike the dative, the prepositional strategy is semantically transparent, since ad ‘to’ has a clear allative meaning; accordingly, its gradual expansion in the functional domain of ditransitivity is expected to follow a revealing path of decreasing semantic motivation, where metaphorical transfers played a major role in the increasing spread of the construction from classical Latin onwards. The Merovingian data discussed in this study add further details on the historical drift towards the grammaticalization of a/à in Romance. In such diatopic variant of late Latin, the gradual extension of the prepositional construction to third arguments of ditransitive verbs continues along the same semantically constrained path identified in earlier stages, but occasionally spreads to additional types of verbs which do not imply any kind of movement. The data discussed in this chapter thus witness a transitory phase where we begin to get glimpses of a substantial shift towards the grammaticalization of the indirect object as a void grammatical relation in Romance languages.