Which Union corps was routed on July 1 by Ewell's attack?

The Union XI Corps was routed on July 1, 1863, when Richard Ewell’s Confederate Second Corps attacked north of Gettysburg. The XI Corps had arrived to support the Union position after fighting began west of town, but its exposed placement made it vulnerable to attacks by Robert Rodes’s and Jubal Early’s divisions.

Although some XI Corps units resisted fiercely, Confederate pressure broke the Union line around Barlow’s Knoll and forced the corps to retreat through Gettysburg. The withdrawal became one of the most dramatic Union reversals of the battle’s first day. The nearby I Corps was also heavily engaged and suffered severe losses, but the question specifically identifies the corps routed by Ewell’s attack: the XI Corps.

The retreat did not end the battle. Union troops rallied on Cemetery Hill and Cemetery Ridge, strong defensive positions south of town. Elements of the XI Corps later helped defend Cemetery Hill, where Early’s Confederates launched another attack that evening. The corps’ poor reputation after earlier defeats also contributed to the criticism directed at its commander, Oliver O. Howard, even though the tactical situation was extremely difficult.