From the 13th-century Icelandic saga of Snorri Sturluson

There was a king named Halfdan the Old, who was most famous of all kings. He made a great sacrificial feast at mid-winter, and sacrificed to this end, that he might live three hundred years in his kingdom; but he received these answers: he should not live more than the full life of a man, but for three hundred years there should be in his line no woman and no man who was not of great repute. He was a great warrior, and went on forays far and wide in the Eastern Regions: there he slew in single combat the king who was called Sigtrygg. Then he took in marriage that woman named Alvig the Wise, daughter of King Eymund of Hólmgard [Hólmgarðr]: they had eighteen sons, nine born at one birth. These were their names:
the first, Thengil [Thengill], who was called Thengil of Men;
the second, Ræsir;
the third, Gram [Gramr];
the fourth, Gylfi;
the fifth, Hilmir;
the sixth, Jöfur [Jǫfurr];
the seventh, Tyggi;
the eighth, Skyli or Skúli;
the ninth, Harri or Herra.

These nine brothers became so famous in foraying that, in all records since, their names are used as titles of rank, even as the name of King or that of Jarl. They had no children, and all fell in battle.