id="id00155">In the whole course of the great river above London there are but three examples of fortification, or at any rate of fortification directly dependent upon the river. Of these the first, at Lechlade, is conjectural; the second, at Windsor, came quite late in history, and the only one which seems to have been a primeval fortified site was Dorchester.

There were, of course, plenty of towns and castles susceptible of defence. At one time or another every important settlement upon the Thames was capable of resistance: Oxford was walled, Wallingford was a fortress, Abingdon or Reading could be defended. But these were all, so to speak, artificial. The settlement came first, and after the settlement the necessity of guarding it from attack, and it was so guarded, not by natural means, but by human construction. The castle at Oxford, for instance, stood upon a mound of earth raised by human work. The only considerable place in which the river itself suggested defence from the earliest times appears to have been at Dorchester.

The curious importance of Dorchester in the very origins of English history and the still more curious way in which it sinks out of sight for generations, to revive again in the tenth century, is one of the puzzles of the history of the Thames.

It is useless to pursue an archæological discussion as to the origin of the place, and still more useless to try and determine why, though certainly the most easily defended, it should originally have been the only heavily fortified spot in the whole of the valley. We know that it was Roman: we know that it was a place of pre-historic fortification before the Romans came: we know that a Roman road ran northward towards Bicester from it, and we also know, or at least we can make a very probable guess, that though it was continuously important, and that the interest of early history is continually returning to it, it can never have been large.