The duchy was nominally a fief of the Polish crown. The County of Flanders was a feudal fief in West Francia. In contrast, Ducal Prussia remained a Polish fief. It was treated as an Imperial fief traditionally granted to Swabian nobles. The Kingdom of Naples was recognized as a papal fief. The Kingdom of Naples was an ancient fief of the Papal States. Naples was a papal fief, which complicated diplomacy. The Norman attacks on Benevento, a papal fief, alarmed and angered Pope Gregory VII. A fief (; ) was the central element of feudalism. The young emperor granted his retirement, but denied the heredity of his fief. Eastern Prussia remained under the Knights but as a fief of Poland. His descendants took their surname from his fief. I was able to seize his kingdom as an escheated fief. In most cases the landowner was sipahi, holder of a fief. Charles later gave the imperial fief of Milan to his Spanish son Philip.