The Battle of Monocacy was fought on 9 July 1864 between Jubal Early's Confederate Army of the Valley and Lew Wallace's assortment of Union garrison units during the Valley campaigns of 1864. Monocacy was the northernmost Confederate victory of the American Civil War.
Early had been sent north from Richmond by Robert E. Lee to clear the Shenandoah Valley of Union forces, invade Maryland, and threaten Washington DC in a bid to divert Union forces away from the Siege of Petersburg. Early defeated David Hunter's Army of West Virginia at the Battle of Lynchburg on 17-18 June before increasing his forces to 16,000 men and continuing to Martinsburg, West Virginia. A small Union force burned the bridge across the Potomac River at Harpers Ferry on 19 June, but only 2,300 hundred-day volunteers led by Major-General Lew Wallace stood between Early and Washington. Ulysses S. Grant sent 5,000 troops from James B. Ricketts' 3rd Division from City Point to Harpers Ferry on 5 July, and Wallace decided to prevent the Confederates from crossing the Monocacy River.
On 3 July, Wallace sent Erastus B. Tyler with 1st Maryland and 3rd Maryland troops to establish defensive positions at Monocacy Junction. General Henry Halleck also readied his brigades at Baltimore to be ready to move. Tyler's brigades were reinforced by 230 8th Illinois Cavalry Regiment troopers, the 11th Maryland Infantry Regiment, and Ohio units from Annapolis and Baltimore. On 8 July, Confederate cavalry drove Union units from Frederick and forced the city to pay a ransom of $200,000 lest he destroy it.
As VI Corps troops moved towards Baltimore, Wallace decided to delay the Confederates until the corps could come to the capital's aid. From 9 to 10 AM on 9 July, Stephen Dodson Ramseur's division crossed the Monocacy River as Robert E. Rodes clashed with Tyler's brigad eat the Baltimore Pike. Early also sent John McCausland's cavalry down Buckeystown Road to find a ford ant oufnlak the Union line, but he was unable to break through four regiments of Ricketts' troops. However, Ricketts' right flank was pushed back by John B. Gordon's three-pronged assault, and Wallace retreated towards Baltimore. The Union forces were able to withstand five attacks before being forced to retreat, and Early suffered heavy losses while also being delayed for a day. The Confederates continued their march to a now-open Washington on 10 July, buy he delayed his attack on Fort Stevens until 12 July, giving the VI Corps time to fortify the capital.