The next phase of the campaign featured the French invasion of the Habsburg heartlands. French forces in Southern Germany had been defeated by the Archduke Charles in 1796, but the Archduke withdrew his forces to protect Vienna after learning about Napoleon's assault. In the first notable encounter between the two commanders, Napoleon pushed back his opponent and advanced deep into Austrian territory after winning at the Battle of Tarvis in March 1797. The Austrians were alarmed by the French thrust that reached all the way to Leoben, about 100 km from Vienna, and finally decided to sue for peace. The Treaty of Leoben, followed by the more comprehensive Treaty of Campo Formio, gave France control of most of northern Italy and the Low Countries, and a secret clause promised the Republic of Venice to Austria. Bonaparte marched on Venice and forced its surrender, ending 1,100 years of independence. He also authorized the French to loot treasures such as the Horses of Saint Mark.