The history of Irish poetry includes the poetries of two languages, one in Irish and the other in English. The complex interplay between these two traditions, and between both of them and other poetries in English, has produced a body of work that is both rich in variety and difficult to categorise. The earliest surviving poems in Irish date back to the 6th century, while the first known poems in English from Ireland date to the 14th century. Although some cross-fertilization between the two language traditions has always happened, the final emergence of an English-language poetry that had absorbed themes and models from Irish did not appear until the 19th century. This culminated in the work of the poets of the Celtic Revival at the end of the 19th and beginning of the 20th century.