In the south, the advance of the West Saxons had been checked in 520, according to the legend, by the prowess of Arthur, king of the Devonshire Welsh. As Mr. Guest acutely notes, some special cause must have been at work to make the Britons resist here so desperately as to maintain for half a century a weak frontier within little more than twenty miles of Winchester, the West Saxon capital. He suggests that the great choir of Ambrosius at Amesbury was probably the chief Christian monastery of Britain, and that the Welshman may here have been fighting for all that was most sacred to him on earth. Moreover, just behind stood the mysterious national monument of Stonehenge, the honoured tomb of some Celtic or still earlier aboriginal chief. But in 552, the English Chronicle tells us, Cynric, the West Saxon king, crossed the downs behind Winchester, and descended upon the dale at Salisbury. The Roman town occupied the square hill-fort of Old Sarum, and there Cynric put the Welsh to flight and took the stronghold by storm. The road was thus opened in the rear to the upper waters of the Thames (impassable before because of the Roman population of London), as well as towards the valley of the Bath Avon. Four years later Cynric and his son Ceawlin once more advanced as far as Barbury hill-fort, probably on a mere plundering raid. But in 571 Cuthwulf, brother of Ceawlin, again marched northward, and "fought against the Welsh at Bedford, and took four towns, Lenbury (or Leighton Buzzard), Aylesbury, Bensington (near Dorchester in Oxfordshire), and Ensham." Thus the West Saxons overran the whole upper valley of the Thames from Berkshire to above Oxford, and formed a junction with the Middle Saxons to the north of London; while eastward they spread as far as the northern boundaries of Essex. In 577 the same intruders made a still more important move. Crossing the central watershed of England, near Chippenham, they descended upon the broken valley of the Bath Avon, and found themselves the first Englishmen who reached any of the basins which point westward towards the Atlantic seaboard. At a doubtful place named Deorham (probably Dyrham near Bath), "Cuthwine and Ceawlin fought against the Welsh, and slew three kings, Conmail, and Condidan, and Farinmail, and took three towns from them, Gloucester, and Cirencester, and Bath." Thus the three great Roman cities of the lower Severn valley fell into the hands of the West Saxons, and the English for the first time stood face to face with the western sea. Though the story of these conquests is of course recorded from mere tradition at a much later date, it still has a ring of truth, or at least of probability, about it, which is wholly wanting to the earlier legends. If we are not certain as to the facts, we can at least accept them as symbolical of the manner in which the West Saxon power wormed its way over the upper basin of the Thames, and crept gradually along the southern valley of the Severn.