A marquess is a nobleman of high hereditary rank in various European peerages and in those of some of their former colonies. The German-language equivalent is Markgraf and the Italian-language equival
Duke is a male title either of a monarch ruling over a duchy, or of a member of royalty, or nobility. As rulers, dukes are ranked below emperors, kings, grand princes, grand dukes, and above sovereign
Marquess
…provinces were set aside for administration by the senate and more unpacified or vulnerable provinces were administered by the emperor. The titles "duke" and "count" were similarly distinguished as ranks in the Byzantine Empire, with dux (literally, "leader") being used for a provincial military governor…
A portrait of James Brydges, 1st Duke of Chandos wearing the robes of the British peerage.
In the 1260s Birger Jarl bore a ducal coronet and used the Latin title of Dux Sweorum (Latin for "Duke of the Swedes"); the design of his coronet combined those used by continental European and English dukes.
Bishop Bengt Birgersson (1254–1291) was the first Duke of Finland