An engraving depicts 18th Corps’ USCT regiments surging into a Confederate Dimmock Line battery on June 15, 1864. As the map indicates, the Federal assaults initially made good headway against the thinly held Rebel defenses, and Petersburg seemed ripe for the taking. But Federal caution and an influx of Confederate reinforcements brought on the months-long Siege of Petersburg. (The Print Collector/Getty Images) The Print Collector/Getty Images