Tilly’s augmented force, with which he threatened to overrun Franconia, urgently required the king’s presence in that circle; but it was necessary to expel previously the Spaniards from the Rhine, and to cut off their means of invading Germany from the Netherlands.  With this view, Gustavus Adolphus had made an offer of neutrality to the Elector of Treves, Philip von Zeltern, on condition that the fortress of Hermanstein should be delivered up to him, and a free passage granted to his troops through Coblentz.  But unwillingly as the Elector had beheld the Spaniards within his territories, he was still less disposed to commit his estates to the suspicious protection of a heretic, and to make the Swedish conqueror master of his destinies.  Too weak to maintain his independence between two such powerful competitors, he took refuge in the protection of France.  With his usual prudence, Richelieu profited by the embarrassments of this prince to augment the power of France, and to gain for her an important ally on the German frontier.  A numerous French army was dispatched to protect the territory of Treves, and a French garrison was received into Ehrenbreitstein.  But the object which had moved the Elector to this bold step was not completely gained, for the offended pride of Gustavus Adolphus was not appeased till he had obtained a free passage for his troops through Treves.

Pending these negotiations with Treves and France, the king’s generals had entirely cleared the territory of Mentz of the Spanish garrisons, and Gustavus himself completed the conquest of this district by the capture of Kreutznach.  To protect these conquests, the chancellor Oxenstiern was left with a division of the army upon the Middle Rhine, while the main body, under the king himself, began its march against the enemy in Franconia.

The possession of this circle had, in the meantime, been disputed with variable success between Count Tilly and the Swedish General Horn, whom Gustavus had left there with 8,000 men; and the Bishopric of Bamberg, in particular, was at once the prize and the scene of their struggle.  Called away to the Rhine by his other projects, the king had left to his general the chastisement of the bishop, whose perfidy had excited his indignation, and the activity of Horn justified the choice.  In a short time, he subdued the greater part of the bishopric; and the capital itself, abandoned by its imperial garrison, was carried by storm.  The banished bishop urgently demanded assistance from the Elector of Bavaria, who was at length persuaded to put an end to Tilly’s inactivity.  Fully empowered by his master’s order to restore the bishop to his possessions, this general collected his troops, who were scattered over the Upper Palatinate, and with an army of 20,000 men advanced upon Bamberg.  Firmly resolved to maintain his conquest even against this overwhelming force, Horn awaited the enemy within the walls of Bamberg; but was obliged to yield to the