Bellarion the Fortunate by Rafael Sabatini

Theodore's sally from Vercelli had been made at daybreak on that Friday morning. It had been shrewdly planned, for Theodore was no bungler, and, before he had brought more than half his men into action, Carmagnola, startled by the suddenness of the blow that fell upon him, was routed and in flight.

After that, this being no more than the preliminary of the task before him, Theodore marched out every man of his following to go against Bellarion at Casale. Thus, by that ancient plan of attacking a vital point that had been left undefended, had Bellarion succeeded in drawing his enemy from a point of less importance in which he was almost impregnably entrenched. Theodore had perceived, as Bellarion had calculated that he would, that it could serve little purpose for him to hold an outpost like Vercelli if in the meantime the whole of his dominions were to be wrenched from his grasp.