Custer's first skirmishes with the Lakota occurred along the Yellowstone River during the summer of 1873, when the Seventh Cavalry served under Colonel David Stanley to protect Northern Pacific railroad surveyors on the river's north side. On August 11, 1873, after the Seventh Cavalry's camp below the mouth of the Bighorn River came under attack, Lieutenant Colonel Custer engaged the Lakota. At dawn, Lakota fighters fired into the troopers' camp from cliffs on the south side of the Yellowstone, then crossed the river in war parties to make a series of attacks and feints against the cavalry. Late in the afternoon, Stanley's infantry companies, including artillery units, arrived, and cannon fire directed across the river finally drove the attackers off. Casualties were light, with one man killed and several wounded, but the Seventh Cavalry spent most of the day in a futile chase of the Lakota. The fighting probably reinforced what Custer and most of his officers already believed about their adversary, that Indians would flee before cavalry attacks, an assumption with fatal consequences three years later. A few days afterward, another skirmish took place near Pompey's Pillar, where the Lakota fired on Seventh Cavalry troopers swimming in the Yellowstone River and forced the naked men to take cover, much to the Indians' amusement. After reaching Pompey's Pillar, the eastern terminus of the 1872 survey, the entire command marched north and surveyed part of the Musselshell River as a possible east-west railroad route before returning to forts in the Dakotas.