There are, indeed, examples of a chain of positions so striking that, from their strength alone, a strategic line imposes itself; but these are very rare. Another, and much commoner, exception to the rule I have stated is the growth of what was once a barbaric stronghold, chosen merely for its position, into a larger centre of population, through which communications necessarily lead, and in which stores and other opportunities for armies can be provided. Such places often preserve a continuity of strategic importance, from civilised, through barbaric, to civilised times again. Laon is an excellent instance of this, and so is Constantine another, and so is Luxembourg a third--indeed they are numerous. But, in spite of--or, rather, as is proved by--these exceptions the fortresses of an organised people are found at the conjunction of their communications, or at places (such as straits or passes) which have the monopoly of communication, or they are identical with great aggregations of population and opportunity, or at least they are situated in spots from which such aggregations can be commanded. Position is always of value, but only as an adjunct. Now Reading, save, perhaps, in barbaric times, when the Thames was the main highway of Southern England, occupied no such vantage until the nineteenth century. To-day, with its large population, its provision of steam and electrical power, and above all, its command of the main junction between the southern and middle railways, Reading would again prove of primary strategic importance if we still considered warfare with our equals as a possibility. But during all previous centuries, since the Dark Ages, Reading was potentially, as it is still actually, civilian; and, indeed, it is as the typical great town of the Thames Valley that it will be treated later in these pages. The long and narrow peninsula between the Kennet and the Thames was an ideal place for defence. It needed but a trench from the one marsh to the other to secure the stronghold. But though this was evident to every fighter, though it is as such a stronghold that Reading is mentioned first in history, yet the advantage was never permanently held. Armies hold Reading, fall back on the town, fight near it, and raid it: but it is never a great fortress in the intervals of wars, because, while Oxford commanded the Drovers' Road, Wallingford the western road, and Windsor (as we shall see in a moment) London itself, Reading neither held a line of supply nor an accumulation of supply, and was, therefore, civilian, though it was nearly as easy to hold as Windsor, as easy as Dorchester, its parallel, easier than Oxford, and far easier than Wallingford, which had, indeed, no natural defences whatsoever. Proceeding with the stream, there is no further stronghold till we come to Windsor.