Complex sentence: The Duke of Clarence was at the gates of St Denis on 9 September 1419, and on the next day the Dauphin had agreed to meet Burgundy on the bridge across the Yonne at Montereau.
Split into simpler sentences: The Duke of Clarence was at the gates of St Denis on 9 September 1419. The next day, the Dauphin had agreed to meet Burgundy on the bridge across the Yonne at Montereau.