Even in his choice of titles— Sonate concertate in stil moderno—Castello demonstrates his confidence in presenting compositions written in an advanced concertato style. In his second book, entitled Sonate concertate, Castello demonstrates his ability to combine virtuosic writing for instruments with a variety of contrasts in sonority and compositional style. The formal ideas often point to a latent sonata form as well as to a formal balance conceived in genuinely musical ways. To this end, certain compositions make use of a significant repetition of episodes as well as a unification and transformation of motifs. The importance of this collection and its dissemination among contemporaries, as witnessed by the reprints in Venice and Amsterdam in 1658, stand in almost inexplicable contrast to the scarcity of biographical information concerning its composer.