other hand, the Life of Methodius directly links Svatopluk's military achievements and Methodius' work. For instance, according to his Life, Methodius promised Svatopluk that if the Prince would celebrate Saint Peter's Day in the Archbishop's church, "God will soon deliver" his enemies to him, and "so it came to pass". Nevertheless, at the court of Svatopluk, who himself professed the Latin Rite, intrigues against Methodius and the liturgy in Old Church Slavonic gathered strength. Svatopluk sent John of Venice, a known opponent of the Slavic liturgy, to Rome in 879 to achieve a settlement of ecclesiastical differences. In a letter addressed to Methodius in the same year, the Pope sharply rebuked him for using Slavonic in church services. Methodius, however, travelled to Rome in 880, together with a Moravian delegation. Under his influence Pope John VIII changed his mind and in a letter, known for its incipit, Industriae tuae, the Pope repeated that Mass was to be sung in Latin whenever requested, but he also allowed the use of Slavonic liturgy. The letter also confirmed the decision taken by the Holy See during Rastislav's reign to create an archdiocese for Great Moravia. Upon Svatopluk's request the Pope promoted a German priest, Wiching, to be Bishop of Nitra, but he added that the new Bishop and all the clerics in Great Moravia were expected to be obedient to Methodius, who remained the head of the church in Svatopluk's realms. The "Wilhelminer War" At the time when Charles the Fat became the sole ruler of East Francia in 881, the sons of Wilhelm and Engelschalk, the one-time commanders of the Bavarian forces occupying Moravia in 870–871, began to conspire with various Bavarian magnates in order to eject Arbo, the margrave Louis the German had appointed to command a key part of East Francia's frontier on the Danube. Arbo, however, appealed for and received help from both Charles the Fat and Svatopluk, and even handed his son over to the latter as a hostage. Upon Arbo's request, Svatopluk, who remembered "how much evil he along with his people had suffered" at the hands of Wilhelm and Engelschalk, attacked their sons. His forces soon captured Engelschalk's second son who was mutilated at Svatopluk's order. Thereafter the remaining sons withdrew from the authority of Charles the Fat and become the men of Carloman's son, Arnulf, who was ruling in Pannonia at that time. Learning of