The Battle of Rio Hill was a skirmish in the American Civil War in which Union cavalry raided a Confederate camp in Albemarle County, Virginia.

During the raid, one of the Confederate caissons exploded, and Custer became confused believing that the explosion was actually the reopening of enemy artillery fire.

Upon arriving at Stanardsville, Custer's men drove off a score of mounted Confederate vedettes in the direction of Orange Court House.

There is some speculation that Moorman initially did not believe the report of approaching Federal cavalry; he received the warning at 12:30 PM, yet his pickets insisted that Rio Mills Bridge was occupied by Union forces when they arrived.

One of Custer's officers recalled that just as the Union cavalry began crossing the bridge over the Rivanna at Rio Mills, four trains were heard moving into Charlottesville.

To buy time, Moorman ordered several pieces from each battery to engage Custer's main force advancing down the Earlysville Road while the rest of his cannon limbered up and withdrew to safety.

At the same time, Captain Ash's squadrons, having completed their crossing at Cook's Ford, rode towards the Confederate camp from the east.

The thin line, armed only with pistols, were tasked with guarding the guns until Moorman could gather forces against Custer's horsemen.

Moorman, recognizing the grave nature of the situation, ordered his artillerymen to mount their battery horses and form into line.

Armed with pistols and sticks picked up off the ground, the mounted artillerymen rode about the four guns still firing into the reforming Federals in the camp.

As his forces withdrew in some confusion into Rio Mills, Federal soldiers burned the bridge over the river behind them to delay the expected Confederate counterattack.

Custer reported of that, over the course of his expedition, his men "marched upwards of 150 miles (240 km), destroyed the bridge over the Rivanna River, burned 3 large flouting mills filled with grain and flour, captured 6 caissons and 2 forges, with harness complete; captured 1 standard bearing the arms of Virginia, over 50 prisoners, and about 500 horses, besides bringing away over 100 contrabands.

In addition to the losses enumerated I would state that the battalion suffered heavily in private effects, especially Chew's and Breathed's batteries."

Though remembered with some sense of local pride as the only noteworthy Civil War engagement in Albemarle County, no effort was made to preserve the location of the camp and the surrounding battleground.

In 1988, a shopping center was built on the precise location of the Confederate camp; subsequent development covered virtually the entirety of the battlefield.