This is the entrance 0f Koutloumousiou seen from the courtyard. On the right side of the porch a pre christian, so called, Grave Stele is part of the wall.
A stele is a stone or wooden slab, generally taller than it is wide, erected in the ancient world as a monument. Grave steles were often used for funerary or commemorative purposes (wikipedia). This Grave Stele is made in the mid-4th century Before Christ. The two figures are unmistakably women. The seated figure is the deceased. The standing woman, probably a servant, is holding a box and offering something to the deceased. This could be an piece of jewelry as it is in the beautiful Grave Stele of Hegeso, dated from ca. 410 – ca. 400 BCE.
The Grave Stele of Hegeso in the National Archaeological Museum in Athens. The jewelry, originally in the hand of the deceased, was painted but has now disappeared.
Part of an article in a German magazine called Antike Welt by Ulrich Hübner about the Pre Christian object in Koutloumousiou. The writer is stating among other things that the Stele is probably placed in the wall a little before the 17th century. Originally the object is coming from Metochia (land elsewhere, owned by the monastery) outside Athos or from the eastern part of Greece.