And now for the part below the small circle, separated from what is above by an open space of clear blue sky. Do you notice that the band of figures stretching across this part takes the form of a curve, repeating the curves of the circles but contrasted with the two important curves of cloud? Its effect is to prevent one’s gaze from soaring altogether upward. This downward curve, as it were, tethers the composition to the ground firmly in the two corners. And now note that the central feature of this lower part is the altar, an equilateral, in strongest possible contrast to the curves and circles above it. That it may have still stronger emphasis, observe how its horizontal lines are repeated down to the bottom of the picture by the steps, so that the eye, as it were, mounts the steps to this central feature. Further the equilateral is again enforced and also balanced by the vertical and horizontal lines, forming a suggestion of equilateral figures in the corners. The one on the right is actually a doorway; the black part is the door. Some artists might have felt it was a drawback to have a bit thus cut out of the picture. Not so Raphael. There, as elsewhere in these rooms, he takes the doorway into his composition and makes it serve a very useful purpose of emphasising the corner, and then invents another structure to strengthen equally the corner opposite.