The exact date at which the plan was undertaken we do not know, but it is obviously one with the scheme of building Windsor, and must date from much the same period.  The order to build was given by the Conqueror to the Bishop of Rochester, Gundulph.  Now Gundulph was not promoted to the See of Rochester till 1077.  Exactly twenty years later, in 1097, the son of the Conqueror built the outer wall.  The Keep was then presumed to be completed, and at some time during those twenty years it must have been begun, probably about 1080.  That which we have seen increasing, the military importance of Windsor, diminished the military importance of the Tower, until, with the close of the Middle Ages, it had become no more than a prison.  It was not indeed swamped by the growth of the town, as was its parallel the Louvre, but the increase of wealth (and therefore of the means of war), coupled with the correspondingly increased population, made both urban fortresses increasingly difficult to hold as mediaeval civilisation developed.

The whole history of the Tower is the history of military misfortune, which grows as London expands in numbers and prosperity.  It probably held out under Mandeville when the Londoners (who were always the allies of the aristocracy against the national government) besieged it under the civil wars of Stephen; but even so there was bad luck attached to it, for when Mandeville was taken prisoner he was compelled to sign its surrender.  Within a generation Longchamp again surrendered it to the young Prince John; he was for the moment leading the aristocracy, which, when it was his turn to reign, betrayed him.  It was surrendered to the baronial party by the King as a trust or pledge for the execution of Magna Charta, and though it was put into the hands of the Archbishop, who was technically neutral, it was from that moment the symbol of a successful rebellion, as it had already proved to be in the past and was to prove so often again.

It was handed over to Louis of France upon his landing, and during the next reign almost every misfortune of Henry III. is connected with the Tower.  He was perpetually taking refuge in it, holding his Court in it:  losing it again, as the rebels succeeded, and regaining it as they failed.  This long and unfortunate tenure of his is illumined only by one or two delightful phrases which one cannot but retain as one reads.  Thus there is the little written order, which still remains to us for the putting of painted windows into the Chapel of St John, the northern one of which was to have for its design “some little Mary or other, holding her Child”—­“quandam Mariolam tenenten puerum suum.”  There is also a very pleasing legend in the same year, 1241, when the fall of certain new buildings was ascribed to the action of St. Thomas, who was seen by a priest in a dream upsetting them with his crozier and saying that he did this “as a good citizen of London, because these new buildings were not put up for the defence of the realm but to overawe the town,” and he added this charming remark:  “If I had not undertaken the duty myself St. Edward or another would have done it.”