Italy was invaded by the Lombards under leadership of their king Alboin less than two decades after the war between the Byzantine Empire and the Ostrogothic Kingdom known as the Gothic Wars (535-554). The Lombards initially settled in Pannonia and helped the Avars destroy the Kingdom of Gepids in 567 but feeling threatened by their former allies Avars they invaded northern Italy one year later.
The Lombards conquered Pavia after a three year siege in 572 and made it capital of their kingdom. From the northern Italy they penetrated deep into central and southern Italy where they established two independent duchies: the Duchy of Spoleto and the Duchy of Benevento. The Adriatic coast from Istria to Numana, the territory from Ravenna to eastern Emilia known as the Exarchate as well as the territory from Rimini to Ancona known as the Pentapolis, the duchy of Rome, the duchy of Naples, Apulia, Calabria, and the islands and coast of Luguria and Tuscia remained in Byzantine hands. The Lombards did not succeed to conquer whole Italian peninsula which was divided on two parts: the Lombard Kingdom and Romagnia. In addition, the Lombard Kingdom itself was divided on several duchies with wide autonomy which weakened the kingdom’s unity and the central power.
Alboin who was murdered in 572 was succeeded by Cleph who was murdered as well only after 18 months of rule. Cleph’s death was followed by a decade of anarchy, plundering and persecution of the Roman population until the accession of Authari (584-590) who defeated the Frankish forces of Childebert II and strengthened the monarchy. He was succeeded by Agilulf (590-616) whose reign was marked by a pro-Byzantine politics and beginning of the Lombard conversion into Catholicism. The conversion into Catholicism was greatly encouraged by queen Theodelinda who was personally very devoted to the Pope Gregory the Great.
Integration of the Roman population and the Lombards began after the death of Rothari (636-652) who was the last Lombard King loyal to Arianism and to the Germanic tradition. The Lombard Kingdom reached its height under the reign of Liutprand (712-744) who took advantage of weakened Byzantine authority in Italy and conquered the Exarchate and Pentapolis and invaded the northern Latium in 728. Liutprand’s conquests disturbed Pope Gregory II, and the Dukes of Spoleto and Benevento. Both dukes decided to submit to Liutprand who also reached a peaceful agreement with Papacy with the so-called Donation of Sutri. Latter granted the city and some hill towns in Latium to the Papacy as a gift to the blessed Apostles Peter and Paul. The conflicts were renewed during the pontificate of Pope Gregory III who concluded an alliance with dukes of Spoleto and Benevento, while Liutprand continued territorial expansion on expense of the duchy of Rome and directly threatened the Papacy. Gregory III turned for help to Charles Martel who needed the Lombard aid for his campaign against the Muslims. For that reason Martel promised the Pope only general support and forced Gregory’s successor Zachary to meet with Liutprand. He returned the conquered territories to the Holy See in 742.
Liutprand’s successor Ratchis (744-749) yielded to the Papacy but his successor Aistulf (749-756) was determined to conquer whole Italy and attacked Exarchate, captured Comacchio, Ferrara, Ravenna and the Duchy of Spoleto. Aat the same time Pope Zachary gave his support to Pepin the Short at his accession to the Frankish throne. Pepin who was grateful for papal support promised Pope Stephen II military assistance against the Lombards and return of all lost territories (Promissio Carisiaca). He kept his promise, invaded Italy and defeated Aistulf and gave the former Byzantine territories to the Papal States with the so-called Donation of Pepin.
Aistulf’s successor Desiderius (756-774) initially led a friendly politics towards Papal States and Frankish Kingdom but eventually he renewed the politics of his predecessor and turned against Rome. Pope Handrian I appealed to Pepin’s son Charlemagne who decisively defeated the Lombards and proclaimed himself the King of Franks and Lombards in 774.