In addition to central North Africa, Malta, Sicily and southern Italy became part of the Aghlabid domain. They considered themselves as vassals of the Abbasids, although with great autonomy, and they maintained their links with Baghdad – the Abbasid capital – with many commercial and scientific convoys despatched and received, including one that brought back the lustre tiles used to decorate the mihrab (prayer niche) of the Great Mosque of Kairouan. In return for Aghlabid loyalty, the Abbasid Caliph al-Musta‘in (r. 248–52 / 862–66) ordered the construction of the dome above the mihrab in the Great Mosque of Zaytuna.