By the last quarter of the seventh century the Byzantine areas of Italy had experienced over a century of upheaval. Within decades of their first invasion of Italy in 568 the Lombards had established a powerful kingdom consisting of the territories north of the river Po, Tuscany and the two outlying duchies of Spoleto and Benevento. The empire was confined to the areas of Rome and its duchy, Ravenna, and the neighbouring areas of the exarchate and the Pentapolis, approximating to the present-day Romagna and Marche, and a few coastal areas elsewhere. The Byzantines had only been able to hold on to their possessions by initiating a thoroughgoing militarisation of society, which involved the concentration of land in military hands and the concentration of authority in the hands of the commander-in-chief in Ravenna (the exarch) and his subordinates (duces and magistri militum at a provincial level and tribuni in the localities). In many areas, such as the Roman Campania, this process was accompanied by a steady shift of population, as settlement became concentrated on military strongholds and refuges, usually located on promontories. Although the pressure eased somewhat in the seventh century, Liguria and most of the remaining settlements on the Venetian mainland were lost to the Lombards in the reign of King Rothari (636–52), and the duchy of Benevento made continual encroachments in the south, accelerating after the unsuccessful expedition of Emperor Constans II (641–68) to southern Italy in 663–8. Internal tensions were reflected in a series of revolts, the determined opposition led by the papacy to Constans II’s monothelite doctrines and a bitter conflict between the sees of Rome and Ravenna over the same emperor’s grant of ecclesiastical autonomy (autokephalia) to the latter in 666. In two letters addressed to his successor, Pope Agatho (678–81) bemoaned the dislocation caused by the ‘gentiles’ and complained that lack of food forced the clergy to work the land.