 Several modern states still trace their own sovereignty to recognition in medieval papal bulls.The sovereignty of the Holy See was retained despite multiple sacks of Rome during the Early Middle Ages.Yet, relations with the Kingdom of Italy and the Holy Roman Empire were at times strained, reaching from the "Diploma Ottonianum" and "Libellus de imperatoria potestate in urbe Roma" regarding the "Patrimony of Saint Peter" in the 10th century, to the Investiture Controversy in 1076–1122, and settled again by the Concordat of Worms in 1122.