One of the particular characteristics of Russian verse is its high level of rhythmic flexibility, attributable to a high frequency of pyrrhic feet. This research attempts to reconstruct how this situation was built on earlier periods of the development of Russian verse. Its results place in doubt the classic notion that the prevalence of pyrrhic feet arose out of the substantial length of the Russian word. A comparison of how the rhythm of iambic tetrameter developed in Dutch, German, and Russian verse shows that the level of metrical flexibility does not depend on the average length of the rhythmic (phonetic) word in a language. The historical conditions surrounding the emergence of syllabotonic verse and the evolution of versification clearly played a decisive role in the prevalence of pyrrhic feet in Russian verse.