Complex sentence: French dragoons crossed the Rhine secretly, surrounded his house and brought him to Strasbourg (15 March 1804), and thence to the Château de Vincennes, near Paris, where a military commission of French colonels presided by General Hulin was hastily convened to try him.
Split into simpler sentences: French dragoons crossed the Rhine secretly, surrounded his house and brought him to Strasbourg (15 March 1804), and thence to the Château de Vincennes, near Paris. There a military commission of French colonels presided by General Hulin was hastily convened to try him.