Guiscard himself had received the title Duke of Sicily (dux Siciliae) in 1059 from Pope Nicholas II as encouragement to conquer it from the Muslims.

In 1061 the first permanent Norman conquest (Messina) was made and in 1071, after the fall of Palermo, the capital of the emirate and future capital of the county, Guiscard invested Roger with the title of count and gave him full jurisdiction in the island save for half the city of Palermo, Messina, and the Val Demone, which he retained for himself.

[5] According to historians Agostino Inveges and Matteo Camera, Roger I started to use the title "Great Count of Sicily and Calabria" since 1096.

Through the mediation of Pope Calistus II and in return for aid against a rebellion led by Jordan of Ariano in 1121, the childless William ceded all his Sicilian territories to Roger and named him his heir.

When William died in 1127, Roger inherited the mainland duchy; three years later, in 1130 in Palermo, he merged his holdings to form the Kingdom of Sicily with the approval of antipope Anacletus II.