 Kemeys was killed when Chepstow Castle was stormed on 25 May, and Powel was taken prisoner when he surrendered Tenby Castle to Horton on 31 May, but Pembroke Castle was a very strong medieval fortress which could not be taken as quickly.It stood on a rocky promontory surrounded on three sides by the sea, and on the landward side its defences consisted of a deep ditch and walls up to thick.Ships carrying siege artillery to Cromwell were forced back up the Bristol Channel to Gloucester by storms, so Cromwell tried a frontal assault.