Shortly after 10 a.m., the head of General Irvin McDowell's flanking column reached Matthews Hill after slow progress as rookie soldiers frequently broke ranks to rest, some stopping to pick blackberries. More than 13,000 Union troops lagged behind schedule and stretched for nearly six miles, with the rear of the column still on the Warrenton Turnpike east of the Stone Bridge when the vanguard emerged from the woods and collided with Confederate skirmishers atop Matthews Hill. After both sides exchanged brief volleys of musket fire, soldiers of the 2nd Rhode Island Infantry deployed and started across the field toward the crest of the hill, ending McDowell's chance at surprise as the battle began.