Battle of St Fagans The Battle of St . Fagans was a pitched battle in the Second English Civil War in 1648 . A detachment from the New Model Army defeated an army of former Parliamentarian soldiers who had rebelled and were now fighting against Parliament . Background . In April 1648 , Parliamentarian troops in Wales , who had not been paid for a long time and feared that they were about to be disbanded without their arrears of pay , staged a Royalist rebellion under the command of Colonel John Poyer , the Governor of Pembroke Castle . He was joined by Major - General Rowland Laugharne , his district commander , and Colonel Rice Powell . Colonel Thomas Horton with a detachment of just under 3 , 000 well - disciplined troops from the New Model Army , was sent by Sir Thomas Fairfax to secure south Wales for Parliament and to crush the rebellion . He had one and a half regiments of Horse ( cavalry ) , most of Colonel John Okey ' s regiment of Dragoon s and most of a regiment of Foot ( infantry ) . Horton at first advanced westwards through Wales towards Carmarthen , but then had to march hastily to Brecon to forestall an uprising there . From Brecon , he then marched south to Cardiff , occupying the town before the Royalists could do so . His force took up quarters in and around St . Fagans , west of the town . Another army under Oliver Cromwell himself was also marching towards Wales . Laugharne was anxious to defeat Horton before Cromwell could reinforce Horton ' s detachment . After a brief skirmish on 4 May , he launched an attack on 8 May . Laugharne ' s army consisted of about 7 , 500 infantry but only 500 cavalry . The Battle . A stream known as the Nant Dowlais separated the two armies . In the early morning , Laugharne sent 500 infantry across the stream to attack Horton ' s centre , hoping to take the Parliamentarians by surprise inside the village . This advance guard was routed by a charge by some of Horton ' s cavalry , and the Parliamentarians were able to deploy in the open . The battle now became general in the open area to the north west of the village . In the centre , high hedges hampered Horton ' s horsemen , but Okey ' s dragoons forced both Royalist wings back . Eventually , Parliamentarian horse under Major Bethel were able to make a charge against the Royalist left and rear . The Royalists panicked and broke . Over 200 of Laugharne ' s men were killed and another 3 , 000 were taken prisoner . The legend that the river Ely ran red with blood may be an exaggeration given the casualties , but the veteran parliamentarian advantage in horses meant they were able to repeatedly rout numerically superior numbers on the Royalist side . Aftermath . Laugharne retreated with what was left of his army to join Colonel Poyer at Pembroke while Colonel Horton marched to besiege Tenby Castle which was held by about 500 Royalists under the command of Colonel Rice Powell . Cromwell , with another detachment of three regiments of foot and two regiments of horse of the New Model Army , had reached Gloucester on the day of the battle and proceeded to cross into South Wales 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 . When these fortresses fell , Cromwell was able to march back into England to defeat an invading Scottish army at the decisive Battle of Preston . Although they had imposed considerable delay , they would have been able to do so even longer if Laugharne ' s field army had not been effectively destroyed at St . Fagans .