It would be difficult to find an aspect of eighth-century papal history that has been more thoroughly studied than the early pontificate of Hadrian I (772–795). A host of scholars—among them Duchesne, Caspar, Kleinclausz, Kehr, Halphen and Hodgkin—have scrutinized each of the highly significant developments which unfolded between Hadrian's election on February 1, 772, and Charles the Great's assumption of the Lombard crown in June, 774: Hadrian's vigorous measures against the Roman supporters of the Lombard king, Desiderius (757–774); his appeal to Charles for Frankish military assistance to counter Desiderius' offensive in the papal duchy of Rome; and Hadrian's conference with Charles in Rome in April, 774, which resulted in Charles' donation of 774 and his subsequent deposition of Desiderius and installation of himself as rex Langobardorum.