150 years ago today Union General John Buford and his First Cavalry Division rode into Gettysburg around 11:00 am. Not much before that some rebel infantry, unsupported by the rest of their division/corps, had left Gettysburg to avoid engaging the stronger Union force.
Buford sent out scouts in hopes getting a better fix on the Confederate forces that seemed to be to his northeast, north, and west. To his south, three Union army corps were prepared to support him should his commander, Gen. Meade, choose to stand his ground at Gettysburg. Another option would be to fall back toward Emmitsburg where the rest of the Army of the Potomac would prepare defensive positions on favorable ground and hope that Lee would continue the attack there. By late evening on the 30th, Buford and his scouts had developed and forwarded to Meade a very accurate picture of Lee's forces.
While everyone acknowledges Buford's skill and courage as a general, there seem to be at least two schools of thought regarding how prescient he was regarding the battle to come. One gives him great credit for choosing the defensive terrain that the Union Army would take and hold while the Army of Northern Virginia battered against it. The other claims Buford was most interested in holding the crossroads of Gettysburg itself and the eventual siting of the Army of the Potomac was due to factors other than Buford's influence.
Whichever was the case, it was clear that Buford expected to be attacked the next day by rebel forces far stronger than his own, and he knew it was going to be a tough fight to hold on until infantry support would arrive. He set to the task of preparing his men accordingly.