He began his work quickly. Within four years of Hastings, and long before the conquest of the Saxon aristocracy was complete, he held his Court at Windsor and summoned a synod there, and, though we do not know when the keep was completed, we can conjecture, from the rapidity with which all Norman work was done, that the walls were defensible even at that time. Of his building perhaps nothing remains. The forest to the south, with its opportunities for hunting, and the increasing importance of London (which was rapidly becoming the capital of England) made Windsor of greater value than ever in the eyes of his son. Henry I. rebuilt or greatly enlarged the castle, lived in it, was married in it, and accomplished in it the chief act of his life, when he caused fealty to be sworn to his daughter, Matilda, and prepared the advent of the Angevin. When the civil wars were over, and the treaty between Henry II. and Stephen was signed, Windsor ("Mota de Windsor"), though it does not seem to have stood a siege, was counted the second fortress of the realm. Of the exact place of Windsor in mediæval strategy, of its relations to London and to Staines, and all we have just mentioned, as also of the great importance of cavalry in the Middle Ages, no better example can be quoted than the connected episode of April-June 1215, which may be called--to give it a grandiose name--the Campaign of Magna Charta. It further illustrates points which should never be forgotten in the reading of early English history, though they are too particular for the general purpose of this book--to wit, the way in which London increased in military value throughout the twelfth and thirteenth centuries; the strategic importance of the few old national roads as late as the reign of John, and that power of the defensive, even in the field, which made general and strategic, as opposed to tactical, attack so cautious, decisive action so rare, and when it _was_ decisive, so thorough. This book is no place wherein to develop a theme which history will confirm with regard to the aristocratic revolt against the vice and the genius of the third Plantagenet. The strategy of the quarrel alone concerns us.