In September 991, when Otto III was eleven, Slavonic raiders captured the city of Brandenburg. In 992 this invasion, as well as an incursion of Viking raiders, forced Otto III to lead his army against the invaders, and he suffered a crushing defeat in this campaign. The next year, Germany suffered an outbreak of famine and pestilence. In 994 and 995, Otto III led fruitless campaigns against the northern Slavs and the Vikings, but he did successfully re-conquer Brandenburg in 993, and in 995 he subdued the Obotrite Slavs. In the fall of 995, after Otto III reached his majority, he again took to the field against the Lutici, this time aided by the Polish Duke Bolesław I the Brave. Then in 997 he had to deal with a new Lutician attack on Arneburg on the Elbe, which they managed to retake for a short while. Reign as emperor Roman instability Prior to his sudden death in December 983, Otto II had installed Pietro Canepanova as pope. Calling himself Pope John XIV, Canepanova was a non-Roman from Lombardy who had served as Otto II's chancellor in Italy. After Otto II's death, John XIV intervened in the dispute between Henry II of Bavaria and Theophanu over the regency, issuing an edict ordering Henry to turn Otto over to his mother. During that turmoil, the Roman aristocracy saw an opportunity to remove the non-Roman John XIV and install a pope from among themselves. The Antipope Boniface VII, who had spent nine years in exile in the Byzantine Empire, joined forces with Byzantine nobles in southern Italy and marched on Rome in April 984 in order to claim the papal throne for himself. With the aid of the sons of Crescentius the Elder — Crescentius II and John Crescentius — Boniface VII was able to imprison John XIV in the Tomb of Hadrian. Four months later, on 20 August 984, John XIV died in his prison, either starved or poisoned, probably on the orders of Boniface. With Otto's regency seated in Germany, Crescentius II took the title of Patricius Romanorum (Patrician of the Romans) and became the effective ruler of Rome, although he did not act entirely independently of central authority, presenting himself as a lieutenant of the king. When Boniface VII died in 985, Pope John XV was chosen to succeed him. Although the details of the election are unknown, it is