The first two of these considerations are very sharply defined not only in their nature, but also in the historical periods over which each one predominated. The Thames as an avenue of ingress or invasion belongs to the earlier part of English history. The importance of the lower river in this category ends very nearly with the close of the Dark Ages. Its second character, that of an obstacle to the invader who would go northward or to troops marching from the north southward, in the main is discoverable of course throughout history, but chiefly belongs to the Middle Ages and the seventeenth century. I will take these three points, therefore, in their order and deal first with the invasions of England which the Lower Thames has served. These invasions from the first recorded case of the almost to the last may be grouped together under one description. They were the raids of the pirates. It is true that these raids became, as the Dark Ages developed and the true Middle Ages approached, better and better organised, more definitely political and dynastic in plan, until at last they took on the character of regular warfare. But from the beginning to the end of the process we have little or no use of the Thames on the part of regular forces proceeding from the ancient civilisation of the Continent, from Gaul, or from the mouths of the Rhine. The whole story is a story of invasion from the outer and barbarian limits of Europe, that is, from the North Sea and the confines of the Baltic. The early pirate raids upon this island, which were first called Saxon, hundreds of years later Dane, but which had through the whole of the Dark Ages much of one character of purposeless devastation, used the Thames for one of their chief entries. The earlier and less powerful raids seem to have made nothing of London. It was too much for them. But the later and worse tempest of the eighth and ninth and tenth centuries had London for their main object when they forced the river, and since it is a piece of history very little explored, it is worth a moment’s digression here. What were the conditions under which the pirates conducted their raids upon the waterway? First let us establish a little list of what was certainly known with regard to these attempts. Of the first Saxon raids in connection with the Thames we know nothing. Even the distorted legends set down hundreds of years afterwards only preserve a recollection of a landing in Kent, in Thames, and the fighting that follows them is upon land and south of the river. Of what raids were made upon the Essex shore, or whether any were made, or whether (which is improbable) any attempt were made by these sparse destroyers against the walls and bridge of London, all the part, small or null or whatever it was, which the Thames played in the first pirate raids of the fifth and sixth centuries escapes us. [Illustration: HAMPTON]