The extent of Wrightsville and the nature of the ground required a line of defense over 1 mile in length. To garrison this line we had Colonel J. G. Frick's Twenty-seventh Pennsylvania Militia (excluding artillery and bridge guards), 650; York Battalion (invalids and Patapsco Guards), 238; Lieutenant Colonel William H. Sickles, 3 companies Twentieth Pennsylvania Militia, 200; total, 2, 088. These troops were disposed of as follows; The Twenty-seventh Pennsylvania Militia, Colonel Frick commanding, occupied the rifle-pits in front and on both sides the York turnpike, with one company thrown forward on the pike to picket the road. The York Battalion (composed of old soldiers, wounded, and convalescents, who have been under fire) was placed under command of Lieutenant-Colonel Green, Twenty-seventh Pennsylvania Militia, and posted on the left of Colonel Frick's regiment, extending to the Susquehanna River, the Patapsco Guards in reserve. This line was most likely to be seriously assailed, as the ground here most favored the enemy's approach. The battalion of Twentieth Pennsylvania Militia, Lieutenant-Colonel Sickles commanding, guarded the approaches on the right of the Twenty-seventh Pennsylvania Militia to the river. The Adams County Cavalry were thrown forward on the York pike and neighboring heights to ascertain if the enemy approached, and their probable force. About a dozen were sent forward to observe the Old Baltimore road. The City Troop patrolled Wrightsville, and obliged every soldier to repair to his company. A few of the City Troop were selected as messengers, and stationed with the field officers to carry communications. My information represented York as having been occupied at 10 a. m. by 1, 000 rebels, and our scouts were driven within our lines without having ascertained the enemy's number or that they had artillery. There was reason to hope that their number was not formidable, and we might save the bridge. However, as the enemy approached, they presented a deployed line of cavalry and infantry skirmishers, which spread to the summit of the ridge on our left, and in the distance a mass of infantry was observed. The enemy advanced very slowly, feeling their way, and occasionally firing, which our men returned. The luxuriant grain in the fields in our front and the woods on our left covered the assailants, while our rifle-pits protected our men; hence the firing did but little injury. For casualties I have to request that battalion commanders be called upon for reports. As the firing began, I received a telegram* from Colonel William B. Thomas, Twentieth Pennsylvania Militia, at Bainbridge, Pa., which is herewith inclosed (marked B), saying; "A scout just arrived from York reports the enemy advancing on Columbia with three brigades of infantry and one regiment of cavalry. If you, " &c. This I deemed it my duty to show to Colonel Frick. The colonel advised retreat, but, dreading confusion when retreating with inexperienced militia, I proposed to the colonel to destroy the span of the Columbia Bridge, thus cutting off all hope of retreat by that route, and hold our ground as long as practicable. We had previously arranged that if cut off from the bridge our retreat should be along the hills bordering the Susquehanna River to some ford above Wrightsville.