There are albums that are so fundamental to a genre’s development, and so inspirational to the bands that discovered them, that it can be hard to view them with clear eyes in the present day. That’s the case with Cave In’s debut album, Until Your Heart Stops. Released in 1999—though often mistakenly credited as having come out in 1998, to the point where the album’s Wikipedia page lists both years—Until Your Heart Stops in many ways feels like the first real metalcore album. And while it’s easy to have a negative, knee-jerk reaction to that descriptor, laying the blame for every bad Trustkill Records act at Cave In’s feet would be like blaming The Buzzcocks for, on a long enough timeline, birthing All Time Low.

With time booked at GodCity—the upstart studio run by Converge guitarist Kurt Ballou—the band was prepped for the session, even if they were still accounting for their gaps in personnel. They’d been using fill-in bass players for a while (one of which was Piebald’s Travis Shettel), until Caleb Scofield, fresh off the break-up of his band Strike 3, agreed to play bass. But just two weeks before Cave In was set to record, their vocalist abruptly quit. Instead of delaying the session or scrambling to find a singer, Brodsky opted to take up the position, whittling Cave In down to a four-piece. But even as they finalized their lineup at the zero hour, they’d be joined in the studio by some of their closest friends and collaborators.

Formed the year those albums were released, Cave In’s early works were not particularly exceptional. Their splits and EPs showed a young band attempting to find their place in the genre while still struggling to solidify their lineup. Guitarists Stephen Brodsky and Adam McGrath, along with drummer John-Robert Conners, would be Cave In’s backbone in that gestational period, guiding the band with a set of influences that pulled from metalcore’s early canon without ever being beholden to it. By 1998, the band appeared to be settling into a groove, finally stable enough to enter a studio and record their debut album.

By the early 90s, these approaches would begin to merge, getting saddled with the term “metalcore” in the process. The genre would become a buzzword, but it was still nebulous enough to rope in bands who, looking back on it now, had little overlap. Whether it was Rorschach’s noise-soaked passages that fell somewhere between bands on Amphetamine Reptile and Ebullition, Earth Crisis’ extension of Judge’s mid-tempo militarism, or the Charles Manson-worshipping of Integrity that gifted the genre with nihilistic occultism, bands were rarely aligned musically, much less ideologically. By 1995, metalcore would see some of its most foundational texts laid down, such as Integrity’s Humanity is the Devil, Earth Crisis’ Destroy the Machines, Acme’s …To Reduce the Choir to One Soloist, and the post-Rorschach band Deadguy’s Fixation on a Coworker. And while no two sounded exactly alike, they’d all help establish what would come next.

Formed in Massachusetts in the early 90s, Cave In took a few years to find themselves. Fittingly, the band’s journey of self-discovery was running parallel to hardcore’s own identity crisis. In the late 80s, the once warring tribes of hardcore and metal began to crossbreed, the result of which was crossover thrash, a faster, more technical subgenre that was gaining prominence up and down the West Coast, with bands like Suicidal Tendencies and Cryptic Slaughter helping bridge that gap. Meanwhile, on the East Coast, bands were creating their own hybrid of metal and hardcore, making a darker, mid-paced sound typified by the Cro-Mags and Carnivore.

“Moral Eclipse” opened the album with a bit of showmanship from Brodsky and McGrath. Until then, metalcore had largely been made up of hardcore musicians stretching their limited skills as far as they could go, but here, the pair dashed off harmonized fretboard runs without batting an eye. Where metalcore guitarists of the past had known a Metallica riff or two, Brodsky and McGrath sounded like they’d spent their adolescence studying the solo to Van Halen’s “Eruption.” Those opening guitar heroics bore more than a passing resemblance to Slayer, but when flanked by the band’s pummeling hardcore attack, it showed they were injecting something new into this mixture of genres. Most importantly, it showed Brodsky’s strength as a frontperson and vocalist—though Bannon’s inhuman shrieks certainly helped set a disquieting mood, too.

When Cave In entered GodCity that April, Brodsky had been playing bass in Converge for over a year, as well as with Ballou in the side-project Kid Kilowatt. It made sense that Ballou would contribute to Until Your Heart Stops, especially given that it was one of the first projects he’d take on at his newly minted studio. But the album quickly became a family affair, as Converge vocalist Jacob Bannon contributed vocals, as well as their former bassist, Shettel, and featured a complementary soundscape designed by Agoraphobic Nosebleed’s Jay Randall. Until Your Heart Stops was the product of collective will, less a singular statement from a band and more a declaration from a budding scene.

This ideological foundation would cause Cave In’s closest allies to make their own sweepingly ambitious works in the years that followed. Converge already had a pair of great albums in their arsenal, but over the next few years, they retooled their approach. The result would be their defining work, 2001’s Jane Doe. Though Brodsky wouldn’t be a part of the writing process for the album, the fact that Converge so willingly downshifted, and incorporated actual choruses into their chaotic compositions, allowed them to take their most ambitious stride up to that point. And since then, the band has never stopped reinventing itself .

If Until Your Heart Stops had ended there, it would have already established Cave In as the frontrunner of this new scene. But the album’s density was matched only by its expanse. “The End of Our Rope is a Noose” and “Until Your Heart Stops / Segue 2” each clock in over the eight-minute mark, and the album closer, “Controlled Mayhem Then Erupts,” is just shy of 14 minutes. These sections were arguably unlike anything to have happened yet in metalcore. They owed great debts to prog-rock, as well as spacier alt-rock bands like Hum, and until that point, hardcore had never dealt in these kinds of reprieves. These calculated segues and lengthy instrumental passages belied Cave In’s aggression, making those heavy mosh parts all the more impactful when they followed endless guitar loops, synthesizer-based compositions, and even an electronic noise piece.

But “Juggernaut” was the first hint that Until Your Heart Stops wasn’t solely concerned with aggression. The song was the most meticulously arranged, with parts coming in seemingly at random but never feeling alien. Every change in tempo, and every new riff, was fundamental to the song’s identity, allowing the band to soften their approach without losing their forward momentum. But it was in the midsection that the band threw in its most cunning trick, with Brodsky and McGrath playing ascending lead runs in complementary keys. Masterfully produced by Ballou, the notes ping between channels as if they were hocketing , allowing the guitarists to create a guitar passage that would be nearly impossible to replicate.

The two tracks that followed, “Terminal Deity” and “Juggernaut,” were further proof of Cave In’s creative genius. In a hair under 11 minutes, the band constructed one of the most densely powerful suites in all of hardcore. “Terminal Deity” showed that the band’s metal influence wasn’t relegated to guitar theatrics, as Conners stepped up and showed a mastery of double bass runs that made the band’s breakdown parts leap out of the speakers. And when Cave In transitioned into groove-based chugs, they could change tempos and moods in a way their predecessors only dreamed of.

But the influence of Until Your Heart Stops wasn’t relegated to bands. The production style Ballou mastered on the record would help him become an in-demand producer. As much as his work with his own band would encourage people to record with him, Cave In gave him his first real break, and he’s outright said as much . Similarly, Bannon’s work on the album’s visual design would give him his first iconic album cover. Until then, Bannon had been finding his aesthetic as a visual artist, and Until Your Heart Stops looked like little else in the hardcore world. Where hardcore album covers had long leaned on cartoon-like illustrations or simple, evocative photographs , Until Your Heart Stops was cleaner and more ambiguous. Featuring an off-center, grayscale heart and a largely black background, the cover didn’t even include the album’s title, making it impossible, at least at the top, to know what the record would sound like when you actually spun it.

And though Tacoma, Washington’s Botch had already built a name for itself, the release of We Are the Romans in 2000 showed they were paying attention to what was happening on the other side of the United States. Guitarist Dave Knudson’s riffs were nimble in a way that showed he was pulling from similar source material as Brodsky and McGrath. But more than that, the songs had a melodic bent that suited the band well, wringing hooks out of vocalist Dave Verellen’s burly shouts. And, of course, the fact it had its own 11-minute piece that dovetailed into electronic loops and Gregorian chanting proved they had taken something from Until Your Heart Stops.

Until Your Heart Stops began to resonate outside of Massachusetts, too. New Jersey’s The Dillinger Escape Plan was already perfecting its version of math-rock-influenced metalcore, and 1999’s Calculating Infinity proved that, but their 2002 EP Irony is a Dead Scene, along with 2004’s Miss Machine and 2007’s Ire Works, would see them expanding outward, into compositions that pulled from electronic music and prog-rock. And while those pursuits are not unique for bands to explore, Cave In laid the blueprint for how to do so while retaining a sharp musical bite.

Speaking of running a concept into the ground, the vocal style Brodsky worked with on this album—guttural screams that blended seamlessly into actual singing parts—would become the most rote hallmark of metalcore over the next decade. By the time the genre became a profitable pursuit for bands, this hybrid of throaty chest-beating flanked by angelic choruses would become the most watered down element in the genre’s history. It’d be a trait linking nearly every band that could find a home on the undercard of both Ozzfest and the Warped Tour, many of whom were able to pivot those sounds into a bit of mainstream success. Bands like Underoath would neuter this sound and get their album Define the Great Line to number two on the Billboard charts, and Killswitch Engage would nab a Grammy nomination for their cloyingly emotional track “The End of Heartache.” By then, the genre had broken down into its most basic parts, turning it into the kind of artistic dead-end that emo had become, with that genre’s progenitors often distancing themselves from it at all costs.

But just as metalcore was hitting it big, Cave In had seemingly lost interest in it. On 2000’s Jupiter, the band went full-on space rock, a move that would split the band’s fanbase in two. Some appreciated the more melodic sensibility, one that was there on Until Your Heart Stops but was now the fulcrum of the band’s sound, and others decried them as sellouts. The band would sign to RCA in the wake of Jupiter, but, by then, they’d gone full-on alt-rock. As a result, their major label debut, Antenna, was even more simplified and radio-friendly, with Brodsky describing it as “the big, slick rock record we spent way too much time and money making,” just a few years later.

After Antenna, Cave In dropped a few more records, each one striking a balance between their harder-edged early years and the catchier elements of their early 2000s work. The band spent the bulk of the past decade inactive, though in 2017, they began working on new material again. In 2018, Scofield, whose bass work provided Until Your Heart Stops with its Earth-rattling undertone, tragically died in a car accident, and Cave In would play a pair of shows with Converge’s Nate Newton on bass to benefit his family. Those tribute shows were massive affairs, seeing Cave In playing alongside their friends in Converge, Pelican, and even featuring a reunion of the post-metal greats ISIS.