Byzantium's interaction with the west appears chiefly political and cultural. In Byzantine eyes western Europeans' Christianity still created the basis for special relations with the empire. The upheavals of the seventh century had transformed Byzantium. Broader economic structures had once spanned the Mediterranean and fostered Byzantine commercial interaction with the west. Constantinople took the diplomatic initiative in order to defend its own vital interests on its western flanks, especially in Italy. Diplomatic interaction fostered cultural ramifications. The several dozen embassies which travelled between Constantinople and western courts constituted privileged intermediaries and much cultural exchange bears their stamp. Like political ones, cultural contacts between Byzantium and the west pivoted on Italy. Carolingian claim to have restored the Roman empire, despite brief periods of mutual acceptance, constituted a permanent challenge to all that was essential to the Byzantine identity. The stage was set for the co-operation and competition that would mark the future of Byzantium's interaction with the west.