This paper interprets persuasively on side as representational medium in architectural planning of lineamentum in Alberti's architectural theory. We made the interpretation, on the basic nature that our previous paper has clarified of the lineamentum, by analyzing the use of perscriptio among his architectural, picture and sculpture theories. The result is as the following; the side of the lineamentum is, essentially, the representational medium (signum) that represents analogically the geometrical representational medium (perscriptio). It is, so to speak, semi-geometrical figure, more simply, figure. But the figure actualizes with the lineamentum at the two scenes that is meant by limbus.
