The object of this study is the case marking of the subject in early medieval charter Latin. The work explores whether and how the nominative/accusative-type morphosyntactic alignment changed into a semantically motivated (active/inactive) alignment in Late Latin before the disappearance of the case system. It is known that the accusative originally the case of the direct object extended in Late Latin to the subject function in which Classical Latin allowed only the nominative. On this basis, it has been postulated that in Late Latin the nominative/accusative contrast was (re)semanticized so that the nominative came to encode all the Agent-like arguments and the accusative all the Patient-like arguments. The study examines which semantic and syntactic factors determine the selection of the subject case in each subject/finite verb combination in the Late Latin Charter Treebank (LLCT). The LLCT is an annotated corpus of Latin charter texts (c. 200,000 words) written in Tuscany between AD 714 and 869. The central result of the study is that the Latin of the LLCT shows a semantically based morphosyntactic alignment in those parts of nominal declension where the morphological contrast between nominative- and accusative-based forms is morphophonologically intact. The following picture of intransitivity split turns up: the low-animacy subjects of the LLCT occur more often in the accusative than do the agentive high-animacy subjects. Likewise, the accusative percentage of SO subject constructions is higher than that of A/SA subject constructions. The common denominator of the examined semantic variables is likely to be the control exercised by the subject over the verbal process. Syntactic factors seem to influence the case distribution pattern as well. For example, the immediate preverbal position of the subject implies a high retention of the nominative. The immediate preverbal position of SV(O) language is a canonical subject position where the syntactic complexity measured as dependency lengths is at its lowest and the cohesion of the verbal nucleus at its highest. Thus, a by then already marked nominative form results. The control of the subject over the verbal process (semantic variable) and the cohesion of the verbal nucleus (syntactic variable) may be partly conflated, i.e., both may affect the subject case selection in certain conditions.