By the summer of 1864 both armies had fully learned a hard lesson: entrenched infantry could destroy almost any frontal assault.

Entrenchments, also called works or fieldworks, are dug-in defensive lines: a trench scraped into the dirt with the spoil thrown up in front as a rampart, so a man can stand in the hole and fire over the top while almost nothing of him shows. By 1864 every infantryman carried a rifle (a musket with a grooved barrel that spun the bullet, accurate and lethal at hundreds of yards, far past the old smoothbore). Put those two facts together and the arithmetic is merciless. A defender behind a dirt wall is nearly invisible and can reload in cover. An attacker making a frontal assault, charging straight at the works across open ground, is fully exposed, on his feet, slowed by every fence and ditch, for the whole long minute it takes to cross the killing zone. Worse, a well-built line is laid out so its sections cover each other: when you charge one stretch of trench, the trench off to your side fires into the length of your line. That sideways, raking fire down the flank of a charging column is called enfilade, and it is the deadliest thing on a Civil War battlefield, since you cannot see where it is coming from and you cannot shoot back at it. Charging good works was, by 1864, close to suicide, and the men in the ranks knew it better than the generals did.

The race for the crossroads opened on May 31, when Major General Philip Sheridan’s (North) cavalry seized the Old Cold Harbor junction in the late afternoon and held it, dismounted, against Confederate pressure until the infantry could come up. On June 1, Major General Horatio Wright’s (North) VI Corps (a corps was a Civil War army’s largest building block, a major formation of many thousands of men, written in Roman numerals as a kind of ID, so VI is simply the 6th) arrived in the morning, and Major General William F. “Baldy” Smith’s (North) XVIII Corps, on loan from the Army of the James, a second, smaller Union army operating closer to Richmond and distinct from the Army of the Potomac that Grant rode with, came up in the afternoon. That evening, around 6:30, Wright and Smith threw themselves at the forming Confederate line, gained a little ground, and broke nothing. Sharp, bloody, inconclusive.

June 2 was the quiet turning point of the whole battle, a day on which almost nothing happened, which is why it mattered so much. Grant wanted to attack, but Major General Winfield Scott Hancock’s (North) II Corps was late: his men had stumbled in after a brutal all-night march and were in no shape to charge anything. So the assault was postponed a full day. Lee used that day to do the one thing that wins this kind of fight. He had his men dig. All through June 2 the Army of Northern Virginia deepened, connected, and refined an elaborate line of fieldworks, a line that by the time it was finished ran something like seven miles north to south, snaking to take advantage of every swamp and ravine, laid out so its sections could pour enfilade fire across each other’s fronts. And not all of that digging was done by soldiers. Behind the Confederate works, enslaved laborers were put to the shovels, impressed Black men forced to throw up the very rampart that white Union soldiers would die charging. The trench that made Cold Harbor a slaughter was, in part, dug by enslaved hands for the army that fought to keep them enslaved. Every hour the Federals waited, that trench got deeper and the fields of fire got more perfect. June 2 was the day Lee turned the ground into a fort, and Grant let him.