The mosaics of Thessalonika’s monuments (such as the Rotunda, Saint Demetrius and Hosios David [Latomou Monastery]) are among the great masterpieces of Early Christian art. Because of their outstanding design and major artistic value these monuments are included among the most significant of the Byzantine period. The monuments of Thessalonika reveal a continuous artistic exchange with the greatest cultural centres of each era (Rome, Constantinople). The city itself was an important artistic centre, from its foundation and throughout the Byzantine period. Heptapyrgion’s use has changed: it now houses the offices of the Ephorate of Antiquities of Thessaloniki City and two permanent exhibitions.