The expression Patrimonium Sancti Petri, or shorter Patrimonium Petri, meaning 'Patrimony of (Saint) Peter', originally designated the landed possessions and revenues of various kinds that belonged to the Church of St. Peter (i.e. the Pope) at Rome.
Until the middle of the 8th century this consisted wholly of private property, but the term was later applied to the States of the Church, and more particularly to the Duchy of Rome.
Read more about Patrimonium Sancti Petri: Patrimonial Possessions of The Church of Rome, Political Position of The Papacy, Collapse of Byzantine Power in Central Italy, Intervention of The Franks. Formation of The States of The Church, List of Papal Patrimonia, Source