what is the pursuit in this book?

When Marcus is wounded, he decides to rescue the totem of his father's Lost Legion, the "unlucky Ninth." Accompanied by Esca, Marcus travels amongst the barbarians disguised as an oculist. The two retrieve the Eagle from an Epidaii tribe and make a mad dash for the safety of Hadrian's Wall. Much of this section involves the pursuit od the Epidaii tribe of Marcus and Esca.