][2] Nothing is known of Castellaneta before 1080, when it was taken by Robert, Duke of Tarentum, who expelled its Byzantine inhabitants.

At this time, possibly, the episcopal see was created;[3] in 1088 Tarentum was made a metropolitan see, and the diocese of Castellaneta was placed under his authority.

[4] In 1088 Riccardo the Seneschal, nephew of Robert Guiscard, who happened to be Lord of Castellaneta, granted to the diocese several monasteries and churches which were under his control.

[6] In December 1100, Amuris, Bishop of Mottola and Castellaneta, who had been given the Church of Castellaneta to rule by Archbishop Alberto of Taranto, granted the Church of S. Matteo Apostolo to the monastery of Cava, with the permission of Duke Roger and Riccardo Siniscalco.

It appears that the diocese of Castellaneta was vacant, and that the Archbishop had assigned its administration to Amuris; the alternative theory is that Archbishop Amuris united the two dioceses, but such an action is a papal function.