The Guy in the WeedsOr perhaps the vines, but he's out there wandering the roads, barefoot and apparently beset upon by a siren.
The design of the vines is extremely complex; especially intricate are the overlapping and intertwined sections. It would be an interesting study to determine whether this entanglement is documentation of local contemporary viniculture, it appears to this untrained eye to be a practical application. The guy himself is well developed: the folds in the clothing, the articulated toes, the curls in the hair and beard, the grasping hand, the entire composition is a demonstration of skill and creativity. Mind you, much of the marble used in this cathedral was quarried from Roman necropolis sites, so it is likely that the artisans saw similar pieces done by their predecessors and there is mimicry in play. Roman sarcophagi were often panels filled with character and complex background imagery. This work is nevertheless a "masterpiece" in that it has all the technical and creative aspects of the work of a sculptor with substantial abilities.
He's out there alone, a pilgrim working his way across the medieval landscape, meandering through a tangled thicket of vines filled with temptation and obstacles.