Byzantine poetry evolved from metres using ancient prosody, like the hexameter, towards forms based on stress accents, notably fifteen-syllable verse. The last hexameters in the living tradition date from the 7th century, the first fifteen-syllables from the 10th. This chapter examines three situations: the declining hexameter, the 300 year gap between the metres, and the emerging fifteen-syllable. The first shows hexameters visibly developing in response to prosodic change, to increase metrical elegance while ensuring the hexameter was still heard as poetry. During the gap, care is required to prevent distortion of historical narratives by choice of poems studied and methodologies used. Early fifteen-syllables probably represent textual adoption of an oral metre. Thus for centuries it is unclear whether changes in written poetry are contemporary evolution, or the written inclusion of more oral poetics, revealing earlier details. The picture is changing after recent discoveries about popular poetry of the 13th century.