I used the word 'septentrionis' for 'of the north' because the Romans referred to the north in this way. The septentriones were the seven stars near the North Pole belonging to the Great Bear. Or the Little Bear. Whichever. You could also use 'boreas'. It is all good.
Some people might object to calling Northmen vikings but it seems to have been a common word for sea-farers from Scandinavia especially those with tendencies to piracy and pillaging. The Anglo Saxon version 'wicinga' appears in the chronicle early on. The etymology is uncertain and the word 'viking' itself might not be derived from Old Norse but Old German since people along the northern coasts would be most at risk from their predations especially after the decline of the Frisian navy following Charlemagne's campaigns against them. It should be fun. I just thought I would warn my many followers why my posts will be seeming rather bloodthirsty this fall.