Around 950 AD as the Dalmatian city states gradually lost all protection by Byzantium, being unable to unite in a defensive league hindered by their internal dissensions, they had to turn to Venice for support. Each of the Dalmatian city states needed protection (even from Narentane piracy), based mostly on economic reasons. In the year 1000 AD an expedition of Venetian ships in coastal Istria and Dalmatia secured the Venetian suzerainty in the area, and the Narentines, Slav pirates, were suppressed permanently. In the occasion Doge Orseolo named himself "Duke of Dalmatia", starting the colonial Empire of Venice.