The Thames
and the territory of the Danish invaders — abandons the Thames above bridges altogether, and uses it as a limita- tion in its estuarial part only, up to the mouth of the Lea.
With the definition of exact frontiers for the English counties, however, a process whose origin can hardly antedate the Norman Conquest by many years, the Thames at once becomes of the utmost importance as a boundary.
Its higher and hardly navigable streams are not so used. The upper Thames and its little tributaries for some ten miles from its source are not only indifferent to county boundaries, but run through a territory which has been singularly indefinite in the past. For instance, the parish of Kemble, wherein the first waters now appear, has been counted now in Gloucester, now in Wilts. But when these ten miles are run, just after Castle Eaton Bridge, and not quite half way between that bridge and the old royal palace at Kempsford, the Thames becomes the line of division between two counties, and from there to the sea it never loses its character of a boundary.
It is a tribute to the great place of the river in history that there is no other watercourse in England nor any other natural division of which this is so universally true.
The reason that the Thames, like so many other European boundaries, has come late into the process of demarcation, and
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