Venice was given de facto independence after this leader's negotiations wit
Venice was given de facto independence after this leader's negotiations with Nikephoros I ushered in the Pax Nicephori. The different regions of this ruler's empire were overseen by counts known as centenarii, who were aided by officials called the missi dominici. After the Battle of Fontenoy, this man's grandchildren split his empire into three parts in the Treaty of Verdun. Einhard was the biographer of this loser at Roncevaux Pass. This son of Pepin the Short was crowned by Pope Leo III on Christmas Day in 800 AD. For 10 points, name this Holy Roman Emperor known as the King of the Franks.   
Venice was given de facto independence after this leader's negotiations with Nikephoros
Charlemagne [or Charles the Great or Charles I or Carolus Magnus or Karoli Magnus; prompt on "Charles"]  