The oldest recorded history of the hexaconch rotunda of St. Mary de Platea in Trogir is associated with the memorial text preserved in two versions (Daniele Farlati, Petar Lučić). The written note provides information on the builder (restorer) of the church at the beginning of the 8th century, a relative of Severus the Great – the leader of the citizens of Salona who settled in Split in the 7th century. The author evaluates the validity of this note: he discusses the directions of previous research, transmission of the text, historiographical interpretations, and the archaeological, typological and stylistic context of the church. Through analysis he concludes that the memorial text is not of early medieval provenance; instead he gives a new proposal for its origin: it belongs to the artificial tradition shaped by the older historical narratives within the communal elite of Trogir in the 15th century, which was turned into a written text in the 16th century. He also defines the rotunda of St. Mary as an early medieval building from the beginning of the 9th century (without older phases) which was transformed into a communal church (ecclesia communis) of Trogir in the high Middle Ages. The author attributes to the text the function of creating the illusion of communal patronage of the church in continuity since the early Middle Ages.