k. 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 archaeological 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.

Perhaps the best conjecture upon the origin of Dorchester is that the
stronghold grew up as an out-lier to the great fort over the river at
the top of Sinodun Hill. The exact and regular peninsula between the
bend in the Thames and the mouth of the Thames is obviously suited for
fortification: the tributary flows just to the east of this peninsula,
exactly parallel with the main river beyond, and covers the peninsula
not only with a stream on its east flank, but with a marsh at the
mouth. One can imagine that the conspicuous heights of the Sinodun
Hills were held, from the very beginning of human habitation in this
district, as a permanent fortress, into which the neighbouring tribes
could retire during war, and one can imagine that when the river was
low in summer, and perhaps fordable, the spit of land before it, which
formed an exception to the marshes round about, needed to be protected
as a sort of bastion beyond the stream. This theory will at least
account for the two great ridges of earthwork going from one water to
the other and completely cutting off the peninsula, since it is agreed
these works are earlier than the Roman invasion. Whatever its origin,
the part which Dorchester plays in the early history of England is
most remarkable.

The conversion of England was effected by a process of which we know
far more than of any other series of national events before the Danish
invasions. That p