The mosaic of St Nicholas survives in a conch above the entrance to the narthex of the chapel dedicated to him.

The saint is shown against a gold background strictly full-face, to chest height, holding in his closed left hand a richly-bound Gospel codex, and giving his blessing with his right. He wears a dark blue chasuble and a pallium decorated with gold crosses. The portrait bears the inscription “SAINT NICHOLAS” and is surrounded by a broad frame with repeated schematised acanthus leaves arranged against a background of rhythmically alternating gold, green, dark blue, and rust.

The mosaic of St Nicholas has not survived in good condition: later interventions on the face and clothing, at an unknown period, have adulterated its genuineness⁵³.

The Saint is portrayed with a particularly broad, triangular body, topped by a small head. His face, which is wide with a short schematised beard and a high wrinkled forehead, is rendered as straw-coloured flesh, without gradations or contrasts of shade, with red marks at the bottom of the cheeks. The flat way in which the face is rendered, without the contrasting of tesserae with gradations of colour or shade, makes the mosaic, in terms of quality, unskilled. The same approach can be seen in the rendering of the clothing, which makes the body seem flat and fleshless.

The mosaic of St Nicholas has been dated by Lazarev to the 11th-12th century⁵⁴, while other scholars have placed it in the 13th-14th⁵⁵. In our view, the type of the face and the simplicity and flat character of the ‘painting’ link this mosaic with the mosaic icon of St Nicholas on Patmos (11th century)⁵⁶, the lost mosaic icon of St Nicholas once in Kiev (12th century)⁵⁷, and the mosaic of the Deisis in the Vatopaidi Monastery (early 12th century). More particularly, the flat fashioning of the face and clothing and the choices of colour are reminiscent of the Blessed Virgin and St John the Baptist in the mosaic of the Deisis – features which point to a dating of the mosaic of St Nicholas to the late 11th or early 12th century.