The Concordat of Melfi, dated 23 August 1059, was also concluded to uphold the previous Treaty of Melfi. The agreement was made between Pope Nicholas II, the Norman Robert of Hauteville, known as Guiscard, and Richard I of Aversa. Through this concordat, Robert and his brother Roger I became vassals of the Church and, thanks to this appointment, the Pope legitimised their possessions in the County of Apulia, which was elevated to the status of Duchy of Apulia and Calabria. Robert then became Duke of Apulia and Calabria. In 1061, he began the conquest of Sicily.