What metaphors are used in Purity of Blood by Arturo Perez-Reverte?

In Chapter Nine, we learn that Alatriste's small sword is called a Bilbo, a name likely derived from its origin in the Basque city of Balbao. Balbao is also the birthplace and last name of Inigo. Although, the relationship between Inigo and Alatriste's weapon is not commented upon directly in the text, we can infer that the author inteded to make a metaphorical connection between the two.