William Swinton, Campaigns of the Army of the Potomac

While the three corps named had been sent on the countermarch towards Culpepper, the Third Corps under General French had been left to guard the line of the Rappahannock, and took position at Freeman's Ford, while the cavalry division of General Gregg watched the passage of the Upper Rappahannock at Sulphur or Warrenton Springs. Now Lee, continuing his northward march, on the afternoon of the 12th struck Sulphur Springs, and there crossed his columns to the north bank of the Rappahannock; so that Gregg found himself assailed by the van of the enemy advancing towards Warrenton, and was driven off after having been somewhat severely handled. Of course, on receiving this intelligence from Gregg, the real nature of Lee's movement was instantly disclosed to Meade, who sent an immediate order recalling the three corps from their untimely move on Culpepper. This order found these corps in bivouac on the road to Culpepper, and reached them towards midnight of Monday, when they at once began a rapid retrograde movement to the north of the Rappahannock.

It is easy to see that from this misunderstanding not only was the general retrograde movement to meet the Confederate advance seriously compromised, but the Third Corps, remaining alone on the north bank of the Rappahannock, was thrown quite out of position and exposed to destruction by an overwhelming force. But Lee, unaware of the true state of affairs, did not turn aside to molest that isolated force, but continued his northward movement, and by a night march of the three corps, the different corps of the Army of the Potomac were, on the morning of Tuesday the 13th, again concentrated on the north bank of the Rappahannock.

As on the morning of the 13th the opposing forces were both on the north side of the Rappahannock, there ensued between the two armies a close race—Lee aiming, by a flank march, to strike in on Meade's line of retreat by the Orange