The campaign began unfavourably.  The impetuosity of Saxe-Weimar, who hoped to recover his own principality, induced Valette to cross the Rhine; but he was forced to retire in all haste, and the army suffered terribly in the retreat.  Turenne was in command of the advanced guard, and his courage and activity alone saved the army from complete destruction —­ seizing upon defiles, overthrowing the enemy who barred the passages, and enabling the army to recross the Rhine with numbers diminished only by sickness, fatigue, and hunger.  At the siege of Saverne, Turenne led the French troops to the attack after three repulses, and succeeded in gaining a footing in the town, but received himself a very severe wound in the arm with a musket ball.  During the following year several towns were captured but no decisive operations took place.

In 1638, the Duke of Saxe-Weimar gained some great successes, defeated the Imperialists with heavy loss at Rheinfelden, and besieged Breisach, the key of southern Germany.  The Imperialist army marched to relieve the place, but reinforcements were sent from France under the command of Turenne and Longueville.  Three battles were fought and the Austrians driven off.  After an assault by Turenne, Breisach capitulated, and all Alsace had now fallen into the hands of Saxe-Weimar.  Having been promised Alsace he refused, as Richelieu desired, to hand over Breisach to France; but on the death of the duke in the following year, Richelieu bought over his lieutenants, the French flag waved over the towns of Alsace, and the Upper Rhine became the French frontier.  Turenne returned to court, where he was received with enthusiasm, and was a short time afterwards ordered to Italy to assist De la Valette, who had been faring but badly there.

Matters had not gone there as Richelieu had calculated.  The Duke of Savoy remained true to his engagement with France, but he died in October, 1637.  The Spaniards had captured Vercelli, and the emperor had bestowed the regency of the duchy on the Cardinal of Savoy and on Prince Thomas, brother-in-law of the duchess.  These, supported by the Duke of Modena and the Governor of Milan, the Marquess of Leganez, declared that they were determined to protect the people against the French and to deliver the young duke from French domination.  The duchess implored help from France, and la Valette advanced to her aid.

While in Paris, Turenne had obtained from the cardinal permission to raise a regiment of dragoons and also that a company of dragoons should be attached to each regiment of cavalry.  These troops were not intended to fight on horseback, but were, in fact, mounted infantry, an arm which, after being in disuse for many years, has lately been recognized as a very valuable one, possessing as it does the mobility of cavalry with the fighting power of infantry.  It was at the head of this regiment that the general started for Italy.  The position of affairs in