“Not knowing exactly what had happened to the Pope, and fearing the worst…the clergy of Rome assembled in August 654, after Martin had been gone for more than a year, and elected as Pope Eugenius I…. During that year, therefore, a situation existed unique in the history of the Papacy: two men simultaneously acting as Pope, but neither an Antipope. Eugenius and his electors probably thought that Martin might have resigned, or might even be dead…. But in fact Martin was alive, had not resigned, and was not incapacitated; therefore he was still in fact the Pope (since a Pope cannot be deposed or supplanted without his consent) while Eugenius was in fact simply the ecclesiastical administrator of Rome.”
— Warren Carroll, History of Christendom, vol. 2 page 244.