There's no doubt about it, Arrow is an incredibly successful show and has been from the very beginning. So successful, in fact, that it created what is now known as the Arrowverse. Consisting of four live-action shows, now resulting in yearly crossovers, the Arrowverse is the biggest treatment the DC Universe has ever seen on the small screen, bar none.

Combining the grand mythology of the DCEU with the fun and wit of the Marvel Cinematic Universe, the Arrowverse tells grand comic book adventures on an almost nightly basis, thanks to the four shows that keep it running.

Arrow, The Flash, Supergirland Legends of Tomorrow all have millions of fans on their own, so the Arrowverse in general draws in a ton of viewers every single week.

However, there are things about it that might even surprise the die-hard fan base, from the origins of this TV universe and its flagship show, to blink-and-you’ll-miss-them Easter eggs. Whatever the case, it's time to take a look at the things that might have slipped by most of the core fans.

Here are the 15 Arrowverse Facts Even Die-Hard Fans Don't Know.

15. Flash Would’ve Joined Team Arrow if the Show Wasn’t Successful

Arrow The Flash

People tend to forget that The Flash was never a surefire bet, despite the fact that it’s now known as one of the most wildly popular superhero shows ever. For the CW, it was a huge risk and representative of a change in the climate of comic book shows on television.

Arrow was a very gritty and realistic series, but fans didn’t want everything to be that. Flash was designed to embrace its campy, comic book roots. But this was a character who had only just been introduced on Arrow and there was a concern that it wouldn’t find an audience or would even alienate the audience they already had.

The tentative plan was that if the show wasn’t the success they hoped it would be, Flash would simply be absorbed back into Arrow where he would become a recurring cast member. Of course, they had nothing to worry about as the show was, well, a runaway hit.

14. Oliver Gets Anxious When He’s Not Around His Bow

Arrow - Oliver and Felicity

This is one of the most clever things Stephen Amell has done with his performance as Oliver Queen/Green Arrow. Actors on TV shows, especially ones with the intense schedule of Arrow, rarely get the chance to improvise.

Amell, however, brought a unique physical touch to his performance. Most superhero performances keep their heroic and everyday identities separate, but Amell does a smart thing by introducing a nervous tick to Oliver.

It also makes sense for someone who survived on a desert island for five years and is readjusting to society. Fans might notice that Oliver’s fingers twitch every now and then when he’s not around his bow. It makes Oliver a more interesting character, because it shows him as more of a caged bird who feels suffocated if he’s not leaping off rooftops and shooting arrows.

13. Constantine Wasn’t Meant to be Part of the Arrowverse

John Constantine holding out his arms.

Constantine made its debut on NBC, not the CW. While it won over a devoted audience fairly quickly, that audience always remained relatively small.

Fans admired the series for its comic accuracy, especially after the film of the same name wound up bearing little resemblance to the source material, and especially loved Matt Ryan’s pitch-perfect portrayal of John Constantine. Unfortunately, the show only lasted one season.

While it began life with now CW ties at all, after the show’s cancellation, Ryan’s version of Constantine was introduced to the Arrowverse in Arrow’s fourth season. He will make a return appearance to the universe in live-action this season on Legends of Tomorrow and will even star in his own upcoming animated series set within the Arrowverse on CW Seed.

12. Every Arrow Title is Spoken Aloud During the Episode

This is a fun and interesting tidbit. While Arrow appears to have no set naming conventions for individual episodes (as opposed to every episode of Jessica Jones beginning with AKA, for example), they all share common ground in that every title is actually spoken aloud during the episode itself.

For episodes like “Betrayal” that’s easy, but for episodes like “Honor Thy Father” and “Deathstroke Returns” it gets a little bit trickier.

While it might not be overly noticeable, it seems to be a fun thing for the creative team of the show to toss the episode titles out there and see if any eagle-eyed members of the audience are able to catch them. It’s definitely something for fans to try and keep track of as they watch the show.

11. There Are Several References to Green Lantern Across Multiple Shows

Arrow - Green Lantern Power Battery

The Arrowverse covers a lot of ground. Fans have been treated to multiple speedsters, vigilantes, even aliens like the Martian Manhunter and Ms. Martian, but the Green Lantern Corps is a whole section of the DC Universe that appears to be noticeably absent.

While no Green Lanterns have made their dramatic Arrowverse debut quite yet, fans have been treated to years of teasing and Easter eggs at this point.

For example, a Ferris Air jet is seen during season one of Arrow, an abandoned Ferris airstrip appears multiple times on The Flash, and a “Welcome to Coast City” billboard is also seen on The Flash. 

In addition, Barry makes a reference at one point to a Ferris Air pilot that went missing, which is a pretty direct reference to Hal Jordan himself, and earlier this year, a Green Lantern Power Battery was even seen on Arrow.

10. Arrow Began Life as a Smallville Spin-off

Aquaman, Black Canary and Green Arrow discuss how to deal with Lex Luthor in Smallville

Interestingly enough, people weren’t that surprised when they first heard about a Green Arrow TV show. He might not have been the biggest, most recognizable DC hero, but he had been a regular cast member of Smallville for the successful show’s last several seasons.

Justin Hartley’s Green Arrow was a mainstay of the series by the time it reached its end and if the Smallville legacy was to continue, he was the most likely choice.

While the initial talks talked about doing the show as a spin-off, that shifted gears into a more unique origin story for Oliver Queen. While Justin Hartley was considered, producer Marc Guggenheim said at the time, “We certainly wanted to chart our own course and destiny.”

9. Pied Piper Auditioned to Play The Flash

The Flash: the Pied Piper raises his gauntlets to attack

While Grant Gustin brought charm and wit to the role of Barry Allen, he was not the first one to audition for the part. Andy Mientus was also considered for Barry, but the producers went with Gustin instead-- a choice that many fans were happy with.

Even if he didn’t get to play The Flash, Mientus made an impression and was brought in to play season one villain Pied Piper.

Pied Piper is a former STAR Labs employee with a vendetta against Caitlin, Cisco and Harrison Wells. The fact that he auditioned for a hero might be slightly referenced in season two, when Flash goes back in time and inadvertently shifts the timeline so that Pied Piper becomes a hero and ally to Team Flash instead of continuing down his path as a villain.

8. Legends of Tomorrow Was Designed For A Rotating Cast

While the first season of Legends of Tomorrow takes great care in establishing its cast of characters and building those relationships, from the very beginning the producers made it clear that fans shouldn’t get too attached to anyone or any particular relationship.

This already became incredibly clear in season two, with the introductions of characters like Vixen and Steel to replace members such as Hawkgirl and Captain Cold.

This has to be done in part for scheduling reasons and other behind-the-scenes issues, but it goes a long way toward making the show feel even more like a comic book. No team rosters are ever really set in stone, so to see people swap out and allow for new characters to come in only makes sense.

7. Calista Flockhart Left Supergirl Because the Show Moved to Canada

Many Supergirl fans were disappointed when it was announced that Calista Flockhart would not be returning as a series regular for the show’s second season as it moved to CW.

Cat Grant quickly became a fan-favorite character. Fierce, witty, confident, she was a mentor to both Kara Danvers and Supergirl. She was an integral part of the show’s DNA during its first season, almost automatically making the second season feel like a soft reboot without her.

Flockhart didn’t have any issue with the cast or crew to prevent her from staying on as a regular, though. It was the change in production that made it more difficult for her to return. The first season was shot in LA where it would be much more convenient for her. However, she couldn’t make the schedule work to return as a regular when the series moved to Toronto.

6. Diggle is Named After the Writer of the Comic That Inspired Arrow

Arrow John Diggle

Fans were hesitant when John Diggle was first introduced on Arrow. The series already took liberties with the comic origins. Then they introduced Diggle as a completely new character who was meant to serve as a partner for both Oliver and Green Arrow. However, even if he’s not originally from the comics, Diggle takes very impotant inspiration from the comic book series regardless.

Diggle was named after comic book writer Andy Diggle, who wrote Green Arrow: Year One, the comic that almost single-handedly served as the basis for television series. Arrow borrows so much from that book, as the producers have often noted, and naming this new and important character after the writer was their way of paying homage.

5. Supergirl Was Under Intense Pressure to Live Up to Smallville

Smallville had only been off the air for a few years by the time Supergirl premiered, ending its ten-year run in 2011. In its later years it even introduced a version of Supergirl, who served as a kind of mentor to Clark in teaching him how to fly. The producers were aware that they couldn’t simply do Supergirl as a female version of Smallville. However, neither fans nor the network would want that.

Because of this, they designed Supergirl to be something of a procedural. It’s very much about the crime solving aspect and balancing out the full-fledged superheroics with the emotional drama.

That was an intentional move on their part, to debut their iconic heroine right out of the gate rather than make people wait. Even compared to Arrow and Flash, Supergirl is the only one in which the character receives her name in the first episode.

4. Arrow’s Police Headquarters is Actually the L.A. Public Library

Paul Blackthorne As Captain Lance On Arrow

This is one fact that most people probably don’t know. It’s a small detail, but an interesting one nonetheless. While the DC shows are primarily shot in Toronto, there are exterior shots from all sorts of different locations.

The various shots of the city skylines, for example, are shots of everything from New York City to Singapore. The police headquarters, a regular mainstay of Arrow, is actually the main branch of the Los Angeles Public Library.

Well, the exterior of it is, at least. Inside the police HQ is simply a set, as is the case with most TV shows of this type. There’s something about the building that gives it a fortress-like appeal, which makes it an easy sell to think of as a police station, even if in real life it’s anything but.

3. Melissa Benoist Was the First Person to Audition For Supergirl

Both Flash and Supergirl underwent a lengthy casting process. This makes sense, though, as these are two legendary characters and there was clearly a pressure to get them right. Supergirl actually wound up casting the very first person to audition.

Melissa Benoist was the first person they saw, and while they had a good feeling, they had to make sure of their options and so the casting team wound up seeing thousands of girls for the role before looping back around to Benoist.

There was some hesitance to cast the actress since she hadn’t had much experience at the time, only recently appearing on Glee. However, she brought an optimism to the part that appeared to be exactly what they were looking for, and so she wound up getting the part.

2. Legends of Tomorrow Started Out as an Atom Spin-off

dc-legends-tomorrow-ray-palmer-atom-brandon-routh

Even though Legends of Tomorrow was planned out long before it was officially announced, the producers weren’t sure exactly what they wanted it to be at first. All they knew was that, after the success of Arrow and Flash, they wanted a new spin-off series that could stand on its own and be as different from those two shows as they were from each other.

Initially, they considered a spin-off for Ray Palmer’s Atom, which makes sense as he is another major DC hero who operates on a very different level than the other two.

The idea evolved until The Atom was instead only one member of a team-up show that would be unique in its approach by essentially being a time-traveling Justice League, with a bit of Star Trek flavor for good measure.

1. Central City is Based on Portland, Oregon

It’s nearly impossible to track the location of any city in the DC Universe. Fans have been arguing for decades about the actual locations of Metropolis or Gotham City. Most of the major DC heroes have their own cities in which they operate and serve as the designated protector of those citizens. This is one of the biggest differences between DC and Marvel, which primarily uses real-life locations and centralizes most of its heroes in New York.

It’s Central City that the Flash calls home and while it continues to be some debate in the comics, the TV show seems to have provided a possible answer for the most keenly observant fans.

A map of Central City is shown at one point, but it’s actually a map of Portland with names replaced with notable Central City landmarks. While that doesn’t necessarily set the show in Oregon, it makes the influence on the live-action interpretation of the city pretty clear, especially considering that there are many other times in which Portland landmarks can be seen on the show.

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Can you think of any other facts about the Arrowverse that most fans might not know? Sound off in the comments!