"You're like a troop of cavalry"
Cavalry detail in the Bayeux Tapestry
GNU Free Documentation LicenseCavalry detail in the Bayeux Tapestry - Credit: Dan Koehl

Cavalry, or soldiers fighting on horseback, constitute the third oldest arm of the military. Miles’s choice of simile underscores the idea of the governess entering into deadly combat.

Perhaps it is also significant that his own name means soldier in Latin, suggesting it is he who is pitted against her in battle.