The Summer Country was the ancient homeland of the Sons of Don, an immortal kingdom of enchantment ruled by the legendary Lady Don and Belin, King of the Sun. Long ago, the Sons of Don came on golden ships from the Summer Country, to liberate Prydain from the tyrannical rule of Arawn Death-Lord. The High King, all magically gifted human folk in Prydain must embark for the Summer Country, as the Age of Enchantments came to an end.
Like so many names in The Chronicles of Prydain, the placename the Summer Country can be found in the collection of Welsh legends called the Mabinogion. In the tale "Culhwch and Olwen" (written down in the 14th century but belonging to an earlier period, probably the 11th), the Summer Country is mentioned as one place from which King Arthur gathers soldiers to take to Ireland. The Summer Country is also mentioned in the 12th-century Life of Gildas as the place of origin of Melwas, the knight who abducts Guenevere.