Pepin's gift made the pope a territorial king until 1870
From 756 to 1870 the Papal States—State of the Church—put Italian lands under the pope's sovereign rule. Pepin the Short granted Stephen II former Lombard holdings atop older episcopal estates; by early modern zenith the domain covered Lazio, Marche, Umbria, Romagna, and more.
Sardinia's kingdom swallowed most papal territory by 1860 into nascent Italy, leaving Lazio; in 1870 Rome and the rest of Lazio fell, though the Leonine City was initially spared occupation. For three centuries inside the Roman Empire the Church could not legally hold property, meeting instead in wealthy homes and titular churches.
Plural or singular naming both fit a composite polity more than a personal union. The pope thus wore two hats—pastor and prince—until Italian unification forced the pastoral role back behind Vatican walls.
Property came before sovereignty. A law of Constantine in 321 let the Church own land and returned what had been seized, and later gifts made the Roman Church a great private landowner in Italy and beyond. Justinian's war on the Ostrogoths from 535 to 554 wrecked Italy, and with Byzantine power centred on Ravenna, the pope, as the largest landowner, drifted into governing the country around Rome; Gregory II even excommunicated Emperor Leo III during the Iconoclastic dispute. When Ravenna fell to the Lombards in 751, Rome was cut off and the popes turned to the Franks. In the 10th century Otto I, crowned by John XII, ratified the Diploma Ottonianum as guarantor of papal lands. Even so, the popes never truly controlled their rugged territory, which kept a patchwork of small counties and marquisates, each built around a fortified rocca. From 1305 to 1378 the popes lived at Avignon, and local strongmen such as the Pepoli of Bologna and the Malatesta of Rimini seized nominally papal cities.
Source: Papal States
