Complex sentence: In 1215, at the Fourth Council of the Lateran, the Pope annulled the marriage on this ground; however, Margaret and Bouchard refused to submit: they take refuge at the Castle of Houffalize in the Ardennes under the protection of Waleran, Count of Luxembourg.
Split into simpler sentences: In 1215, at the Fourth Lateran Council, the Pope annulled the marriage on this ground. They took refuge at the Castle of Houffalize in the Ardennes under the protection of Waleran, Count of Luxembourg.