The Merman's Children
Poul Anderson
 Set at the end of the medieval era, The Merman's Children details the end of the last bastion of the kingdom of the Merfolk, one of the Faery peoples being displaced by the advancing tide of Christianity. The city of the Liri king (the Merman of the title) lies beneath the waves off the shores of Denmark, peacefully coexisting with the landbound humans until exorcised by a zealous priest and his churchbells. The majority of the Merfolk are destroyed or scatter, unable to withstand the onslaught, leaving only the king's halfling offspring by a human lover. The story follows them and their various fates as they seek a place to call their own, in locales as varied as the dying Norse colonies in Greenland and the coastlands of Dalmatia.