On 1 June 1192, after Orio Mastropietro abdicated the throne, Dandolo became the forty-first Doge of Venice. He was the second doge to be chosen by a council of forty electors. Already aged and blind, but deeply ambitious, he displayed tremendous energy and mental capacity. His remarkable deeds over the next eleven years have led some to hypothesize that he actually may have been in his mid seventies when he became Venice's leader. None of the earlier chronicles and contemporary witnesses give his exact age, only mentioning that he was very old. The commonly given birth year of c. 1107 is based on the account of Marino Sanuto the Younger (1466 – 1536) three centuries later, who stated that Dandolo was eighty-five when he assumed the throne. Though not the first doge to take the "promissione ducale," Dandolo's is the earliest that is available to historians.