The present papaer discusses proportional relationship between width of arch and that of pillar in the Roman commemorative arch until Julio-Claudian period. Between those width, having no relation with the difference of passages, we perceive simple ratios on intergral number. Among the various ratios, several of them are same in some commemorative arches. In the commemorative arch with three passages, especially, the ratio itself between each axial width of four pillars are common to that in the arch with single passage.
