Ayia Sophia (Holy Wisdom) was once the metropolitan church of Thessalonike; it was built in the 7th century on the site of a large Early Christian basilica with three aisles.
The design of the church, a large dome and arcades on three sides making a single tripartite unit of the narthex and the side aisles, illustrates one of the early stages in the transformation from the architectural type of basilica to the cruciform domed church.
Mosaics of various dates are preserved in the interior. The cross on the sanctuary vault, projected against a blue background and lying in a multi-coloured circle, dates to the period of iconoclasm (8th century). There used to be another iconoclastic cross in the sanctuary apse; it was replaced after the triumph of the iconophiles (843) by an image of the Virgin Enthroned with Christ, a large portion of which fell down and was restored in the 12th century.
The mosaic of the Ascension, executed about 885, is an outstanding example of Byzantine art remarkable for its abstract character and the way in which it is fitted in the space available. The wall-paintings preserved on the intrados of the windows in the narthex portray important monastic figures and are dated to the 11th century. It is a rather conventional work displaying drawing and technical weaknesses and is part of the "painterly" trend which occurred in mid-11th century art.