The Doge of Venice, Giovanni II Participazio, a nepotist intent on continuing the power of his own dynasty, had tried to obtain the government of Comacchio for his brother Badoaro and to this end sent him to the pope.

However, Marinus, count of Comacchio, had captured him and sent him back to Venice, where he soon died.

Giovanni had attacked and devastated Comacchio, but he could not hold it, because it was the pope's.

Charles the Fat signs a treaty with Giovannni in 883, granting that any assassin of a doge who flees to the territory of the empire will be fined one hundred pounds of gold and banished.

King Alfred, because of his support and his donation of alms to Rome, receives a number of gifts from the Pope Marinus in probably 883, though there is some debate over the year.

Among these gifts is reputed to be a piece of the true cross, a true treasure for the devout Saxon king.

According to Asser, because of Pope Marinus' friendship with King Alfred, the pope had granted an exemption to any Anglo-Saxons residing within Rome from tax or tribute.

Pope Marinus I, born the son of a priest, had been ordained as a deacon by Pope Nicholas I.

Before his election as Pope in December 882, he had served as Bishop of Caere, which made his election controversial, because, at this stage of history, a bishop is expected never to leave office to move to another see.

On three separate occasions he had been employed by the three popes who preceded him as legate to Constantinople, his mission in each case having reference to the controversy started by Photius, Patriarch of Constantinople.

Among his first acts as pope had been the restitution of Formosus as Cardinal Bishop of Portus and the anathematizing of Patriarch Photios.

Due to his respect for Alfred the Great, he frees the Anglo-Saxons of Rome from tribute and taxation.

He dies in May or June 884, his successor being Adrian III.