Detail of a hand crossing the border between spirals.
No evidence is available for this source.
The way in which the hand is carved out of the spiral border suggests that the border was carved before the rest of the frieze was completed. In general the architectural framework - including the internal staircase and the laying out of the windows - was planned as a first phase of work and then the spirals were added before work on the carving of the frieze began. The layout of this scene, in which the figures do not quite fit the space available, supports the view that there was no single drawing of the whole frieze from which carvers copied. Rather the carvers seem to have had quite a lot of free reign to fit what was required into the available space.