Four Ancient Books of Wales
The Four Ancient Books of Wales is a term coined by William Forbes Skene to describe four important medieval manuscripts written in Middle Welsh and dating from the 13th, 14th, and 15th centuries. They contain primarily texts of poetry and prose, some of which are contemporary and others which may have originated from traditions dating back to as early as the sixth and seventh centuries.
Source: Wikipedia — Four Ancient Books of Wales (CC BY-SA 4.0)