All metrical verse involves the measurement of the line; in this paper we show that the line is measured by grouping syllables into pairs or triplets (feet), which are further grouped into pairs or triplets. The grouping is accomplished by iterative rules which build a metrical grid from the line. English accentual-syllabic and French syllabic meters are scanned by similar rules; we show that all French meters are in fact organized into iambic feet. The organization into feet and higher-level metrical units (metra and cola) is evidenced in English by the regular rhythms of the metrical line, and in French by the rules of caesura placement.