AbstractThe study carried out in this paper about some new examples of Banach spaces, consisting of certain valued fields extensions, is a typical non-archimedean feature. We determine whether these extensions are of countable type, have t-orthogonal bases, or are reflexive. As an application we construct, for a class of base fields, a norm ║ · ║ on c0, equivalent to the canonical supremum norm, without non-zero vectors that are ║ · ║-orthogonal and such that there is a multiplication on c0 making (c0, ║ · ║) into a valued field.