The land where Lloyd Alexander's Chronicles of Prydain are set is called Prydain. It is a fictional country ruled by a High King and divided into smaller territories and kingdoms known as cantrevs.
The five-book series follows Taran, an assistant pig-keeper who becomes involved in the struggle against Arawn, the evil Death-Lord. His companions include Princess Eilonwy, the bard Fflewddur Fflam, the creature Gurgi, and the dwarf Doli. The stories blend coming-of-age adventure with questions about courage, responsibility, identity, and the meaning of heroism.
Prydain is strongly inspired by Wales. Alexander encountered Welsh culture and landscapes while receiving military intelligence training there during World War II, and he drew on Welsh mythology, geography, and folklore. Many names echo Welsh tradition, including Arawn, Gwydion, and the Isle of Mona, although Alexander created his own characters and story.
Annuvin is not the name of the country: it is Arawn's fortress and the Land of the Dead. The series was published from 1964 to 1968, and The High King won the 1969 Newbery Medal.