DOOM’S FIRST EPISODE, Knee-Deep in the Dead, was constructed according to several themes.

The first and most obvious theme can be found in its aesthetic, and its building blocks. All eight maps—plus a ninth, secret map—unspool across military bases and scientific laboratories stationed on Phobos, one of the two moons of Mars. Computer terminals flash and flicker, factory walls are stained with slime, narrow walkways ring or zigzag over pools of toxic waste, and in the distance, gray mountains huddle beneath overcast skies.

Episode 1’s second theme is size. With two exceptions, each level of Knee-Deep in the Dead is bigger than those that precede it. The exceptions are E1M9, The Military Base, which resembles a tic-tac-toe board; and E1M8, a dimly lit lab where players square off against two of the goat-legged, fireball-hurling Barons of Hell.

The third theme is the episode’s designer. Doom co-creator and id Software co-founder John Romero built every map of Knee-Deep in the Dead except for E1M8. That was constructed by fellow id designer Sandy Petersen, and was much more compact than missions one through seven.

There’s good reason for E1M8’s size discrepancy. Every eighth map in each of Doom’s four episodes is a boss level, and most are designed to be small, moody, and linear—the perfect formula to drive players toward a showdown with one of hell’s big bads.

Still.

To Romero, the first episode’s progression and themes can be summed up in one word: Bigger. Every level boasts more rooms, more courtyards, more passageways. E1M8, consisting of two main rooms linked by a long hallway, is memorable, but breaks the streak of progressively larger environments.

“I thought the final level should be really cool, a long journey, and then end in a really impressive room, and then that's the end of it,” he said. “That's what I would have done.”

In January 2016, just over 22 years since Doom’s release on December 10, 1993, opportunity knocked. “I wanted to get back into level design, that creative mode, because I was getting ready to build a new game and do a pitch,” he said. “I like that kind of game style, so if I was going to make it, I wanted to be back in that space mentally, and possibly move beyond what I'd done before.”

Romero’s pitch was for Blackroom, a first-person shooter inspired by retro FPS titles, namely Quake and Doom. Romero had reunited with another id Software co-founder, artist Adrian Carmack (no relation to John), and was planning to unveil Blackroom on Kickstarter when the time was right.

Before then, Romero wanted to get his level-design legs back under him. He knew just the way to do it: Remake E1M8, the only map of Knee-Deep in the Dead he had never touched, so that it matched his vision for the episode.

Romero had had little choice but to hand the reins over to Sandy Petersen back in ’93. Not only was he busy designing maps alongside Petersen—as well as Tom Hall before Hall left the studio—he was working long hours coding DoomEd, the proprietary editor used to make maps. “It was so much work to make the game, and Sandy was super-fast,” Romero said. “All day long he was making levels, just pounding them out. He'd take pieces of what Tom did, and was finishing them, retexturing them, just getting content done.”

While John Carmack wrote most of the code that powered Doom’s engine—retroactively named id Tech 1, a title Romero considers a misnomer since it implies that Doom’s engine was id’s first piece of tech—Romero handled in-game features. Every time he’d think of a new function specific to level design, he’d stop what he was doing, write code for the function within the game engine, add support for it in DoomEd, bug-test it to make sure it worked as intended, and push out a new version of the editor. That left little time for map-making.

“If a lift moves, if stairs are built, if a light is flickering, if a switch flips, if lava burns you, if a ceiling crushes you—all those things, I programmed them. That took more of my time than pure level design all day long.”

Over two weeks in early 2016, Romero devised his ideal final map for Knee-Deep in the Dead. Dubbed E1M8b, the map would be larger, dwarfing the snarl of corridors and secret rooms found in E1M7’s computer lab before it. It would be dangerous, too, in the spirit of the eighth mission of any Doom episode culminating in all-out warfare against swarms of monsters, a boss demon, or both.

E1M8b opens in a small foyer where an Imp, a leather-skinned demon studded with spikes, and a zombified sergeant stand with their backs to players. Across the room lies a shotgun. As soon as players fire a weapon, or when the Imp and zombie spot them as they attempt to pick up the gun, a cacophony of roars, shrieks, and gunfire explode from every direction, signaling that the level has begun in earnest.

Toxic muck floods many hallways and chambers, making navigation dicey. Players often have to wade through it until they can find a radiation suit to protect them from environmental damage. Enemies seem to come from everywhere. Some hold high ground where they can snipe until players get off a lucky shot or, much later, find their way up to them and enact vengeance with shotgun blasts at close range.

Romero aspired to do more with E1M8b than merely design the episode’s largest map. Throughout his level, players move in and out of rooms and outdoor regions covered in slime. Going between safe to hazardous terrain forces them to adapt to different vantages, sometimes fighting enemies up high in rooms and on ledges, other times running and jumping across rocky ground bordered by a sea of slime that stretches out in all directions. Reaching elevated positions affords them a perspective on the level they haven’t seen before, and offers observant players hints as to where they should go and how they might get there.

“The thing I did in E1M8b was having the player go over the areas that they'd already explored, which is running across the tops of the passages into lower areas,” Romero explained. “That was the only time I did that in any of the original Doom levels.”

Romero knew better than to jettison all of the original E1M8’s brilliant ideas. The map’s lead-up to a climactic battle against two Barons of Hell—known at an early stage of development as the Bruiser Brothers—was perfection. Their arena was just large enough to give both monsters and players space to maneuver, yet tight enough that failing to pay attention to surroundings could result in players backing themselves into a corner. “The Bruiser Brothers were the bosses of Episode 1, and I wanted to make sure I kept Sandy's cool idea of the two coming out of the doors right in front of you. I thought that was cool; I just wanted to make it a little more dramatic,” said Romero.

E1M8b’s boss room takes place in a chamber with just enough room to run around. Two red portals sit side by side in the center, towering over the floor. Players enter the room by way of a narrow ledge high above. Stepping onto it causes the ground to break away and lower them into the boss room, like bait strung to a hook. The only way to escape is to send the Brothers Bruiser back to hell.

Romero delighted in seeing his vision come together. It was the first time since 1995’s The Ultimate Doom, a re-release of Doom featuring Episode 4: Thy Flesh Consumed, that he had built a map for his favorite game. The interface and tools he was using in 2016 were the same as, yet different from, DoomEd in 1993. Id’s developers had written the game and its toolset on Apple co-founder Steve Jobs’ NeXTSTEP operating system, but DoomEd never made the jump to other platforms. Every Doom editor published since had been written from scratch.

To create E1M8b, Romero used Doom Builder 2, a free utility for Windows that streamlines many aspects of creating levels. Romero had not had the luxury of designing a tool as slick and efficient as Doom Builder, written by Pascal vd Heiden—known as CodeImp in the Doom community—and a team of coders and testers who, like CodeImp, developed the editor as a passion project.

“What I made was not made that way,” Romero said in reference to Doom Builder. “The editor [DoomEd] was made for me and Tom—and later Sandy—to build levels.”

Romero’s objective in writing DoomEd had been to code up tools for the designers as quickly as possible. Occasionally, he got to add an advanced feature that only he and his colleagues would know how to fully exploit. One such was the ability to flood a sector—an area with four sides, such as a room or hallway, and able to contain properties such as textures that deal damage—with the elements it needed to operate. Doom Builder’s developers had done that and more, iterating on their creation for years to merge accessibility with advanced functionality. “In Doom Builder, you can just say, ‘make sector,’ and just click, and it makes the sector inside of a room. It's got its own kind of version of what I did in the original, but Doom Builder is so much easier to use,” Romero said.

Romero’s first map in over two decades took shape in just two weeks. On January 16, he uploaded E1M8b to Doom World, one the most popular if not the most popular Doom forums and repositories of free maps and TCs, total conversions that transform the game’s levels, monsters, and items into brand-new assets.

He didn’t expect much to come of the release. In the time he spent on the forums, he knew that fans liked to talk about id’s glory days during the 1990s. Many conversations centered on Romero’s levels. Perhaps, he hoped, a few hundred fans would geek out over seeing a new map made by one of Doom’s authors. “Reading these comments, I thought, It'd be really cool [to let others play the map]. This level-design creativity that I want to restart: Why don't I release levels since people have been asking for them anyway?”

Within hours, thousands of fans had downloaded E1M8b and left reviews. Word traveled beyond the Doom community to the gaming press, who announced that Doom’s most prolific co-creator had returned to the game that had at one point raked in over $100,000 a day for id—a total that only factored in shareware purchases; copies of the full release brought in hundreds of thousands more.

E1M8b sent a message. John Romero was back.

THERE WAS A reason Romero made a new map for Doom rather than returning to another of the games he’d co-designed, such as Quake. “Doom's engine is really easy to use. It's really easy to build for, and it's fast to build for. I was more interested in spending all my time being in a creative space instead of dealing with the hassles of full 3D, which eats up a lot of time.”

Stories of Quake’s arduous development are legendary. According to Romero, he can whip up a single room for Doom in no time: four lines, four seconds—done. Quake’s process is more complex, in part because of the instability of its engine until John Carmack got a handle on programming a true-3D game. Even then, building a skeletal room in Quake required more effort than dropping four lines. Quake’s ace design team of Romero, Tim Willits, Sandy Petersen, and American McGee had had to create brushes, building blocks such as doors, switches, lifts, and other elements that defined a level’s geometry, then placed them according to a very rigid series of steps.

Romero recalled working on an early version of Quake’s E2M6 map. He’d finished half the level when Carmack rolled out a new version of the tech. The update had, among other changes, altered the scale of hallways. “Because of the amount of brushes, the density of geometry, this partial level I'd made at the old scale, I didn't have time to rebuild it, and I had no time to try and fix it: spread it out, pull it apart. It took so long to do that in 3D. The rest of the level feels all right, but the rest feels tighter, and is a little older.”

As Romero wove together E1M8b, he found himself remembering how he did things way back when—squaring off rooms, deciding when and where to place trigger events such as doors opening to unleash a horde of monsters—and carrying out those functions as effortlessly as if December 10, 1993, had been just yesterday.

“It was easy. Instantaneous. No problem,” he said. “The E1M8b you played was exactly what I made [as a first draft]. I didn't do any tests or temp levels, anything before that. I just started making it. It was cool.”

Doom fans around the world tended to agree. “E1M8B is a wonderful map that is all the more astounding for being Romero's first foray back into the FPS mapping world since Quake 1,” wrote one user on Doom World. “If this is just a warm-up, I look forward to seeing what he can do with all cylinders firing.”

Three-and-a-half months later, Romero hopped back in his time machine. E1M8b had been a hit, and he was still putting together designs for Blackroom. As another warm-up exercise, he set his sights on recreating E1M4.

Although Romero received credit for building most of Knee-Deep in the Dead, bits and pieces of E1M4 had been made by Tom Hall before his departure from id Software. Romero had taken those bits, created lots of new architecture to go with them, and finished the level. “This was a chance for me to make a level that would replace that. I wanted to do something new in E1M4,” he said of E1M4b.

The original E1M4’s most distinctive characteristic is a maze near the end. The lighting is dim and spooky. The ceiling is so low players can almost believe they’ll have to crawl rather than run through it, the walls claustrophobically tight. Side passages unravel from the main path, all of which lead to supplies such as health and ammo, as well as encounters with Imps and the bulldog-like Pinky Demons. Other than the maze, Romero said, E1M4 had been just another futuristic lab. Not a bad level by any stretch, but unremarkable aside from its final minutes.

For his re-imagining, Romero wanted to fool players into believing his map was small, only to reveal more as they progress. Every switch they pull, every button they press, and in certain areas, every step they take, peels back layers like an onion. Elevators activate, stairs raise to help players reach previously inaccessible terrain, and walls lower to reveal new paths.

“When you're playing deathmatch, it's cool because everybody eventually pulls as many walls down as possible so they can see through areas and shoot rockets out there, do all kinds of stuff that you could not do at the beginning of the level,” Romero added.

Following another two weeks of off-and-on work, Romero uploaded E1M4b to Doom World. Once again, the gaming press obliged with write-ups, YouTubers uploaded their playthroughs, and Doom World members posted their impressions.

Romero was over the moons, both Phobos and Deimos. Academically, he’d learned nothing new in regard to designing maps. Neither of his new levels was meant to be innovative. They were refinements, distillations of months of coding and decades of daydreaming about Doom maps.

Personally, however, he’d learned an invaluable lesson. He still had it.

“It made those memories come to the forefront, out of the filing cabinet in my head,” Romero described of creating E1M8b and E1M4b. “I don't forget how to program in 6502 assembly language. I'll never forget that. I did it every single day for 10 years. It's part of me, just like making Doom levels is part of me.”

Twenty months later, everything had changed. Romero and Adrian Carmack had launched their Kickstarter campaign for Blackroom, billed as a “return to fast, violent and masterful play on the PC,” per marketing copy, on April 25 with a funding price of $700,000. The campaign had raised over $131,000 over its first couple of days, then flagged.

Part of the problem was that Blackroom’s creators showed nothing concrete. Romero and Adrian Carmack had created masterpieces in the past, but their legacies were not enough. The gold rush of crowdfunded games over 2012 and 2013 were over. Even the most devoted fans of the id duo’s work had expected—and needed—to see more in order to buy into Blackroom.

A few days later, Romero and Adrian put the campaign on ice. They promised to return in the future with a demo boasting “the kind of gameplay, look and innovative, cool features that make Blackroom truly unique—the things we've waited years to put into an FPS.”

All the while, Romero received notification after notification from Doom players who were enjoying his Doom maps. Fans were still leaving comments about his remakes of E1M4 and M8 on YouTube and Doom World. Speed-runs popped up. Romero smiled as he watched them. Back in Doom’s heyday, fans had been able to record in-game demos and share them online, but recording them had required players to type in esoteric commands as they booted up the game. Watching replays had been just as complex. First, Doom fans had to find the replays, a tall order in the days before Doom World and Google. Second, demos could only be viewed from within the same version of Doom that had been used to capture the footage.

“That was always like, ‘Which version of Doom was this recorded with? Is it going to play back on this version of Doom that I have?’ I didn't do that much,” said Romero of watching replays in the ‘90s. “With YouTube, you can just watch. It's immediate, and it's great to hear people talk about it.”

Several fans posted messages wondering if Romero would take the next logical step: Releasing an entire megawad, or a pack of custom levels.

The more he read and the more he watched, the more Romero felt inspired to take that step. By Christmas 2017, he had made up his mind. He would return to designing levels for Doom, but which version? And what would those maps look like? How would they play?

“None of those questions had answers,” he admitted. “It was just this idea: Yes, I will do an episode. I think people will like it, but I need to do even better than E1M8b and M4b.”