Gasa or kasa was a form of poetry popular during the Joseon period in Korea. Gasas were commonly sung, and were popular among yangban women. Chŏng Ch'ŏl, a poet of the 16th century, is regarded as having perfected the form, which consisted of parallel lines, each broken into two four-syllable units. The form had first emerged during the Goryeo period. Gasa was a vocal genre that derived from Jeongga (정가), which consisted of three types of genre. Gagok and sijo were basically poems set to melodies, while gasa were a bit longer than sijo poems. Gasa emerged during Goryeo but became very prominent during the Joseon period. Based on relevant records, it is presumed that this form of verse started to be written after the reign of King Yeongjo. At the very beginning, gasa was meant to be sung. Over time, they became longer and began to be recited instead. Some even consider them to be essays. A gasa can go on, as long as its composer stops writing. The narratives were typically long, and very rarely styled – so it is unclear as to how they were sung due to the different melodies and sounds.