How did cynghanedd develop from alliteration and internal rhyme in Welsh poetry?

Cynghanedd evolved from the foundational prosodic devices of early Welsh bardic verse, specifically the alliteration and internal rhyme present in the works of early poets like Taliesin and Aneirin.12

By the 9th century, these elements were used to embellish metrical forms in saga poetry, appearing as "incipient" cynghanedd alongside alliteration and internal rhyme. Over the following centuries, these techniques were refined and integrated into the traditional bardic craft. By the 13th century, these disparate devices had coalesced into the formal, intricate system of consonant correspondence and internal rhyme known as cynghanedd.21

This system became an obligatory feature of the 24 strict Welsh metres, requiring cynghanedd in every line. Its development culminated in the 14th century with the rise of the cywydd, a verse form popularized by Dafydd ap Gwilym that utilized a stricter version of the device, known as cynghanedd gaeth, to achieve greater linguistic virtuosity. The system was later formally codified at the Caerwys Eisteddfod of 1523.1324