The Lower Thames last appears before the Conquest as an element in warfare when Godwin and his sons enter the mouth of the River in 1052, the fifty ships of the King not daring to offer battle. London favoured this particular advance, allowed Godwin to pass under the Bridge without obstacle (which shows how the masts were stepped), and with that successful but hardly challenged expedition ends the first chapter of the Lower Thames in English warfare: the chapter of its use in the Dark Ages as an avenue of invasion into the heart of the country and against London and, already by the early eleventh century, its strategical value as an obstacle to the movement of troops from north to south. The Lower Thames in the warfare of the Middle Ages, and indeed up to that of the seventeenth century and the Civil Wars--that is, throughout a space of six hundred years (from 1066 to 1644), appears in English warfare only in the character of the main obstacle of crossing South England. It is impossible to develop a negative aspect of this kind at any great length, nor is it even possible to affirm it as an universal negative. I can indeed call to mind no case of the transport of troops in any considerable numbers from the north to the south of the Lower Thames, or vice versa, during the period in question. But even if some considerable exception be discovered, it does not affect the general thesis that the great groups of civil war which marked the history of England in the Middle Ages and during the seventeenth century were powerfully affected in their strategy by the interruption to eastern communications to north and south, which was caused by the Lower Thames and its estuary.