After Earl Patrick's imprisonment, he sent his illegitimate son Robert Stewart to raise a rebellion in Orkney in his favour. Robert seized the Palace of Birsay with thirty companions in May 1614, then occupied the Earl's Palace, the castle and St Magnus' Cathedral in Kirkwall. As many as 700 rebels subscribed to a band which claimed their action was restoring royal justice in Orkney under the direction of Robert Stewart during the Earl's absence. Robert was defeated by a force commanded by the Earl of Caithness at the end of September, after a five-week siege of the Earl's Palace. The Earl of Caithness battered the Palace with 140 cannon shot; he said the castle was so strong that some of his cannonballs broke in two like golf balls. Twelve of Robert's men were hanged at the castle gate.