Colonel Ashton only arrived at Lancaster to find the town partially in ruins; he then marched on to the neighbourhood of Whalley. On the road he was followed by the Earl of Derby and his forces, and a slight engagement took place, after which the Royalists took shelter in the abbey, but were afterwards forced to retreat through Langho Green to Ribchester. Colonel Ashton and his men then proceeded to Padiham, where, "having a good minister, some hours were spent in thanksgiving" for their great deliverance. On April 1, Wigan, one of the headquarters of the Royalists, was stormed and taken after a very short struggle by Colonel Ashton's forces; but, according to Rosworm, owing to some treachery the place was vacated the same night, the soldiers having first taken some prisoners and much spoil, and having placed "great heaps of woollen cloth of the drapers in the streets." Wigan was again taken on April 28 by Colonel Ashton, who, having burnt the gates of the town, took an oath from the townsmen never again to bear arms against the King. Warrington was now garrisoned by the Earl of Derby. It was defended on one side by the river Mersey, which was crossed by a bridge of four arches; over this bridge was a narrow roadway, and on the centre pier stood a watch-house which had formerly been used by the Austin Friars as an oratory. The other sides of the town were defended by mud walls, with gates at the principal entrances; outside these walls outworks had been thrown up. Against this stronghold Sir William Brereton's forces and a large detachment from Manchester laid siege on April 1 (1643), but they only succeeded in getting possession of Sankey Bridge and "a fayre large house of one Mr. Bridgeman's."[143] They withdrew their troops after a three days' siege and some smart fighting, the reason alleged for this being that the Earl of Derby set fire to the centre of the town, and threatened to burn down the whole place rather than it should be taken.