In writing ths narrative, which relates to the decisive campaign which freed the Northern States from invasion, it may not be out of place to state what facilities I have had for observation in the fulfilment of so important a task. I can only say that I was, to a considerable extent, an actor in the scenes I describe, and knew the principal leaders on both sides, in consequence of my association with them at West Point, and, subsequently, in the regular army. Indeed, several of them, including Stonewall Jackson and A. P. Hill, were, prior to the war, officers in the regiment to which I belonged. As commander of the Defences of Washington in the spring of 1862, I was, owing to the nature of my duties, brought into intimate relations with the statesmen who controlled the Government at the time, and became well acquainted with President Lincoln. I was present, too, after the Battle of Gettysburg, at a very interesting Cabinet Council, in which the pursuit of Lee was fully discussed; so that, in one way and another, I have had better opportunities to judge of men and measures than usually fall to the lot of others who have written on the same subject. I have always felt it to be the duty of every one who held a prominent position in the great war to give to posterity the benefit of his personal recollections; for no dry official statement can ever convey an adequate idea to those who come after us of the sufferings and sacrifices through which the country has passed. Thousands of men—the flower of our Northern youth—have gone down to their graves unheralded and unknown, and their achievements and devotion to the cause have already been forgotten. It is, therefore, incumbent upon us, who were their comrades in the field, to do all in our power to preserve their deeds from oblivion.