Complex sentence: He was unaware that the archduke had arrived by forced marches from Augsburg to the vicinity of Ostrach and thought the main force of Charles' army was still three days march away.
Split into simpler sentences: He was unaware that the archduke had arrived by forced marches from Augsburg to the vicinity of Ostrach. Jourdan thought the main force of Charles' army was still three days march away.