How does Rosemary Sutcliff use imagery in The Eagle of the Ninth?

Imagery:

"Strayed cattle; that was all. And yet for Marcus the tension had not snapped into relief. Perhaps if he had never seen the new heron's feathers on an old war spear it might have done, but he had seen them, and somewhere deep beneath his thinking mind the instinct for danger had remained with him, ever since." Chapter 3, pg. 25

"Marcus set his bundle carefully on the table. 'We have brought back the Hispana's lost Eagle,' he said, rather muzzily, and very quietly crumpled forward on top of it." Chapter 19, pg. 230