“Robinson’s Band Plays Anything,” F. Bildestein, 1890. From the cover of the New Orleans newspaper the Mascot (November 15, 1890).

Musical forms have the life cycle of carnivorous beasts: clumsy in infancy, terrifying in adolescence, fearsome in maturity, fangless in old age, and pitiful in senescence, before the inevitable silent death. Their life spans tend to be longer than ours, so it can be difficult to recall that some of the more geriatric genres were once vital and fierce. But even Baroque music had a caddish streak—“a most dangerous reef,” in the words of a prominent seventeenth-century German rector, “along which many a young soul, as if called by Sirens … falls into dissoluteness”—and polka, in the 1840s, was a venal Bohemian menace (in 1844, the Illustrated London News wrote that polka “needs only to be seen once to be avoided forever!”). Jazz, now well advanced into its second century, had an especially violent youth. It was more than merely dangerous—it was homicidal.

Jazz, to be precise, was never extraordinarily ferocious. “Jass” was. The soft sibilant turned heavy at around the same time—a century ago—that the music crossed over in the national consciousness, rumbling north on steamboats up the Mississippi and on the northbound Illinois Central to Chicago, then to New York and California, where it swiftly gained popularity, social acceptance, critical esteem. To do so, it had to leave New Orleans, its native home, behind. This was understandable, given the treatment it had received.

The Times-Picayune, the official record of the city’s white establishment, felt obliged to register its revulsion in an exuberantly racist editorial published during the summer of 1918, entitled “Jass and Jassism.” The music was a “vice,” like the “dime novel” and “the grease-dripping doughnut,” the manifestation “of a low streak in man’s tastes that has not yet come out in civilization’s wash. Indeed, one might go farther, and say that jass music is the indecent story syncopated and counter-pointed.” Jass, that is to say, was sex rendered as music.

Of course, you didn’t need the syncopation or the counterpoint to figure this out. The lyrics of some of the most popular songs put it frankly, numbers like “The Whore’s Gone Crazy,” “Funky Butt,” “The Naked Dance,” and “Cocaine Blues,” which Jelly Roll Morton remembered going like this:

I want a gal that works in the white folks’ yard,
A pretty gal that works in the white folks’ yard,
Do you see that fly crawling up the wall,
She’s going up there to get her ashes hauled.
I got a woman lives right back of the jail,
She got a sign on her window—Pussy For Sale.

The music was free, uncensorable, ecstatic—qualities opposite to the way young African Americans in New Orleans were expected to comport themselves in public, at least by the readers of the Times-Picayune. Such brazenness was alarming. The only solution, the editors concluded, was to choke the young music in its very cradle. The infanticide would be “a point of civic honor,” for “its musical value is nil, and its possibilities of harm are great.”

For the moment, the anti-jassists appeared to have triumphed. By 1918, Jelly Roll Morton had moved to San Francisco; Buddy Bolden, the founding king of New Orleans jazz, had by then already spent a decade at the state insane asylum in Jackson, a hundred miles away; his successor King Oliver, who had worked as a butler to an uptown family while pioneering the new music, had fled to Chicago, where he was followed by many of his former bandmates; one of them, his eighteen-year-old student Louis Armstrong, left town the same year on a steamboat orchestra heading up the Mississippi. The previous year, the prostitution palaces of Storyville, reliable venues for early jazz musicians, had been outlawed, and the outbreak of the Spanish flu emptied the honky-tonks, country clubs, and dance halls. Those musicians who remained found work as painters, longshoremen, or manual laborers. Kid Ory was a carpenter. The bandleader Bab Frank ran restaurants. Alphonse Picou, composer of “High Society,” was a tinsmith.

Many of the musicians lived in a neighborhood so rough it was known as the Battlefield. The streets were unpaved, strewn with broken glass, nails, oyster shells. The children, invariably, went barefoot. “But we were young, healthy and tough as old hell,” Louis Armstrong wrote in his memoir Satchmo, “so a little thing like lockjaw did not stay with us a long time.” Once, as a young child, while playing in one of the abandoned, ramshackle buildings that served as jungle gyms for the neighborhood children, Armstrong was laid out by a slate tile that had fallen from the roof.

It knocked me out cold and shocked me so bad I got lockjaw. When I was taken home Mama Lucy and Mayann worked frantically boiling up herbs and roots which they applied to my head. Then they gave me a glass of Pluto Water, put me to bed and sweated me out good all night long. The next morning I was on my way to school just as though nothing had happened.

But it was in these same streets that Armstrong, like so many musicians of his generation, heard the new sound—in the second-line parades returning from the cemeteries; in the jangled tunes that junk collectors played on tinhorns; and from the ballyhoo wagons that carried bands through the streets, advertising boxing matches and dances and dueling with other wagons in “cutting contests” when they encountered each other, until the losing band was forced to retreat in shame. The windows to the honky-tonks and dance halls were left open to the street, so even a barefoote urchin could freely listen. If anything, the street audience was given priority: before a band went on stage, it was the custom for them to set up on the sidewalk and perform a free set for those walking by.

A good way to chart the music’s standing in New Orleans during this transitional period is through the story of the Axman, a madman who began hacking people to death in March 1918. The killer’s motivation was murky at first. Most of his victims were Italian grocers and their wives, which may have had something to do with the fact that grocers lived in apartments attached to their stores and were thus easily accessible to a prowler. But the maniac also killed other innocent people, and by summer the randomness of the slaughters, paired with their brutality, had plunged the city into a state of panic. Dozens of suspected Axmen were arrested—most of them black—and released without charge; men fell asleep in chairs propped against their front doors, cradling loaded shotguns.

The hysteria only subsided with the emergence of the Spanish flu, a far deadlier and more conniving serial killer. When the flu subsided in spring 1919, however, the Axman returned in full gore, slaughtering a grocer, his wife, and their infant child. Within a week, he sent a letter to the Times-Picayune, making a startling admission: “I am very fond of jazz music.”

Swearing “by all the devils in the nether regions,” the Axman announced that he would fly over New Orleans the following Tuesday night and murder anyone who wasn’t listening to jazz. That there was a self-evident affinity between jazz fandom and ax killing was understood, the killings a logical manifestation of the music that the Times-Picayune had described as an “atrocity.” But the city’s response to the letter indicated that attitudes were changing. That Tuesday night, there was no fear, only euphoria. Jazz music could be heard all over the city, not just in the Battleground but in the Garden District and from the millionaires’ mansions on St. Charles Avenue. True to his word, the Axman spared the entire citizenry the ax.

Near the end of his life, Louis Armstrong liked to say that jazz dissolved racial boundaries—that, for at least the space of a song, even white bigots were romanced out of their hatred. “These same society people may go around the corner and lynch a Negro,” he told Ebony in 1961. “But while they’re listening to our music, they don’t think about trouble.” It was trouble, though, that had given the music its life. When a music loses its danger, it succumbs to nostalgia, imitation, and charm, qualities of diminishing potency. It would take later generations to reinvigorate the form and, at least for a time, make it dangerous again. Miles Davis even scared himself; in his memoir, he wrote about what it was like when he first played with Coltrane: “Man, the shit we were playing in a short time was scary, so scary that I used to pinch myself to see if I was really there.” He understood what all great artists—including the Axman himself, an artist of the serial murder—understand, that anything truly new, in Jelly Roll Morton’s phrase, puts a fear into the heart.