when did the latter come into power?
1058
Robert Guiscard
Soon after his succession, probably in 1058, Guiscard separated from his wife Alberada because they were related within the prohibited degrees. 
where did the battle of dyrrhachium take place? The battle was fought outside the city of Dyrrhachium, the major Byzantine stronghold in the western Balkans, and ended in a Norman victory. between whom did it take place? The Byzantine Empire, led by the Emperor Alexios I Komnenos , and the Normans of southern Italy under Robert Guiscard, Duke of Apulia and Calabria.
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Robert Guiscard [SEP] Rule
Soon after his succession, probably in 1058, Guiscard separated from his wife Alberada because they were related within the prohibited degrees. Shortly after, he married Sichelgaita, the sister of Gisulf II of Salerno, Guaimar's successor. In return for giving him his sister's hand, Gisulf demanded that Guiscard destroy two castles of his brother William, count of the Principate, which had encroached on Gisulf's territory. The reformist Papacy, at odds with the Holy Roman Emperor (due to the Investiture Controversy) and the Roman nobility itself, resolved to recognize the Normans and secure them as allies. Therefore, at the Council of Melfi, on 23 August 1059, Pope Nicholas II invested Guiscard as duke of Apulia, Calabria, and Sicily.