The Ninth in Brittain's - It's Very Unlikely

In rosemary succles book, and also in the films a centurion and the eagle, the ninth goes into what is now scotland and gets destroyed. That makes no strategic sense. You don't send a legion off by itself because it''s just going to get wiped out. It's just possible this happened an be extremely unlucky if it happened a second time. And we know that the ninth is regularly sections of them are being taken elsewhere to parts of the empire.