Formosus (c. 816 in Ostia–896) was Pope of the Roman Catholic Church from 891 to 896. His brief reign as Pope was troubled, and his remains were exhumed and put on trial in the notorious Cadaver Synod.
As early as 872 he was a candidate for the papacy, but due to political complications he left Rome and the court of Pope John VIII that year. John convened a synod, and Formosus was ordered to return, or be excommunicated on charges that he had aspired to the Bulgarian Archbishopric and the Holy See, had opposed the emperor and had deserted his diocese without papal permission, had despoiled the cloisters in Rome, had performed the divine service in spite of the interdict, and had "conspired with certain iniquitous men and women for the destruction of the papal see" . The condemnation of Formosus and others was announced in July 872. In 878 the sentence of excommunication was withdrawn after he promised never to return to Rome or exercise his priestly functions.
In 883 John's successor, Pope Marinus I, restored Formosus to his suburbicarian diocese of Portus. Following the reigns of Marinus, Pope Hadrian III (884–885) and Pope Stephen V (885–891), Formosus was elected Pope on October 6 891.
Supporters of Guy II of Spoleto forced Formosus to crown him as a Roman Emperor in April 892. Other immediate issues were that in Constantinople, the Patriarch Photius had been ejected and Stephen, the son of Emperor Basil I, had taken the office. There was a quarrel between the Archbishops of Cologne and Hamburg concerning the Bishopric of Bremen. In the contest between Odo, Count of Paris and Charles the Simple for the French crown, the Pope sided with Charles.
Formosus persuaded Arnulf of Carinthia to advance to Rome, invade the Italian peninsula, and take control of Italy. In 894, Arnulf's army occupied all the country north of the Po River. Guido died in December, leaving his son Lambert in the care of his mother Agiltrude, an opponent of the Carolingians. In autumn 895 Arnulf undertook his second Italian campaign, and in 896 he was crowned by the Pope in Rome. The new emperor moved against Spoleto but was struck with paralysis on the way and was unable to continue the campaign.
Pope Stephen VI, the successor of Boniface, influenced by Lambert and Agiltrude, sat in judgment of Formosus in 897, in what was called the Cadaver Synod. The corpse was disinterred, clad in papal vestments, and seated on a throne to face all the charges from John VIII. The verdict was that the deceased had been unworthy of the pontificate. All his measures and acts were annulled, and the orders conferred by him were declared invalid. The papal vestments were torn from his body, the three fingers from his right hand that he had used in consecrations were cut off and the corpse was thrown into the Tiber (and later retrieved by a monk).
Following the death of Stephen VI, Formosus' body was reinterred in St Peter's. Further trials of this nature against deceased persons were banned, but Pope Sergius III (904–911) reapproved the decisions against Formosus. Sergius demanded the re-ordination of the bishops consecrated by Formosus, who in turn had meanwhile conferred orders on many other clerics, causing great confusion. Later the validity of Formosus's work was re-reinstated. The decision of Sergius with respect to Formosus has been subsequently disregarded by the Church.