He arrived in his domain on 27 August and took up residence in the Piazza del Duomo. Spending the bulk of his time in Siena, he was immensely popular among the Sienese. In 1631, he joined the Austrian belligerency in the Thirty Years' War. He took part in the famous battle of Lützen, in November 1632, where he met Sienese General Ottavio Piccolomini.