 Oliver Cromwell with another Parliamentarian army consisting of three regiments of foot and two of horse had reached Gloucester on the day that the Royalist army was routed at the Battle of St. Fagans and proceeded to cross the south Welsh border shortly afterwards.He left Colonel Isaac Ewer in command of a small force to besiege the Royalist garrison of Chepstow Castle which was under the command of Sir Nicholas Kemeys and pressed on to join Horton at Tenby arriving on 15 May.Leaving Horton with enough men to deal with Powel, Cromwell marched the rest of the army to lay siege to Pembroke.