The arrival of the Normans in southern Italy occurred in 1009 AD, but their substantial emigration dates back to around 1030 AD, when the five sons of Tancred of Hauteville – William Iron arm, Drogone, Humphrey, Robert and Roger – came down to Italy from the Contentin peninsula.

Roberto had settled in Sila with a group of faithful, demonstrating his strength, valor and decision through raids, robberies and massacres. In fact, with a stratagem he managed to kidnap a nobleman from Cosenza in exchange for a considerable ransom. It is likely that from this episode he gained the nickname of Guiscardo ("the ") coined by Gerardo di Buonalbergo.

After the conquests of the Normans, the principality of Salerno had lost many domains and power. Guiscardo was now aiming for Amalfi and Salerno. Sichelgaita, daughter of Guaimar IV, understood that her only hope of salvation was in an alliance with the new powerful men, to be realized through her marriage to Roberto.

Anna Comnena (Byzantine princess considered one of the first known female historiographers) describes Guiscardo as thus: «Majestic of face, of tall stature, broad-shouldered, perfect in form, with tawny hair and beard, and lively penetrating eyes: ready and shrewd in intelligence, ambitious beyond measure, mature in his advice, provident in his undertakings, courageous and expert in matters of war, rigorous and prudent in civil government".

He was responsible for the construction of the Norman Castle of Sala Consilina.