The Normans began constructing castles, their trademark architectural piece, in Italy from an early date. William Iron Arm built one at an unidentified location (Stridula) in Calabria in 1045. After the death of Robert Guiscard in 1085, the Mezzogiorno (peninsular southern Italy) experienced a series of civil wars and fell under the control of increasingly weaker princes. Revolts characterised the region until well into the twelfth century and minor lords sought to resist ducal or royal power from within their own castles. In the Molise, the Normans embarked on their most extensive castle-building programme and introduced the "opus gallicum" technique to Italy. Their clever use of the local stone artisans, together with the vast riches amassed from their enslaved population, made such tremendous feats possible, some as majestic as those of the ancient Roman structures they tried to emulate.