Metropolis

Metropolis (メトロポリス) is a recurring location in the Sonic the Hedgehog series. It is the capital city of the Eggman Empire where Dr. Eggman has his central headquarters, and the most heavily fortified of Eggman's fortress. Most of the time however, Eggman has operated out of mobile command centers or hidden research labs rather than Metropolis. Eggman also usually priorities the establishment of the "ultimate city" of Eggmanland, which aesthetically resembled a theme park more than an actual city, but serves the same purpose as the home nation of the Eggman Empire, over Metroplis. Nonetheless, Metropolis has been the site of its fair share of battle between Sonic the Hedgehog (and his allies) and the forces of evil.

Description
Over the years, the overall layout of Metropolis has differed between each depiction. What each depiction has in common though, is that each of them is presented as an enormous metallic capital/fortress of machines and robots.

In Sonic the Hedgehog 2, western sources described Metropolis as Dr. Eggman's "capital city". However, it was actually depicted more like an industrial plant with no real indicator of its actual importance in Eggman's plans.

In Sonic Chronicles: The Dark Brotherhood, Metropolis was shown in a manner similar to an actual headquarter befitting of Dr, Eggman. At that time, Metropolis was a gargantuan machine-city, a polluted nightmare of steel and concrete, replete with robot sentries, Orwellian tele-screens, and free-flowing rivers of radioactive slurry. It was also equipped with various death traps, such as laser torrents, deadly robots and acid traps.

In Sonic Forces, Metropolis differed vastly from its previous incarnations, having either undergone extensive renovations or been rebuild from the ground up in a new location. This version shows Metropolis as a futuristic and pristine but sterile capital with skyscrapers, see-through walkways, and orb-shaped sentries.

Sonic the Hedgehog 2
Metropolis first appeared as Metropolis Zone, the eighth Zone of Sonic the Hedgehog 2; coming after Oil Ocean Zone and preceding Sky Chase Zone. Unlike the previous seven Zones, Metropolis contains three full Acts, and the Zones are particularly massive&mdash;in some cases infinite, for in Act 2, the bottom of the level loops to the top. The boss of this Zone is Flying Eggman.

Sonic Chronicles: The Dark Brotherhood
Sonic Chronicles: The Dark Brotherhood actually starts with the destruction of Eggman's Metropolis. GUN attacks the city in full military force, while Sonic, Tails, Knuckles and Amy battle the Doctor on board his latest Egg Carrier (which bears closest resemblance to the flagship, Final Fortress from the end of Sonic Heroes). Tails succeeds in sabotaging the Carrier, such that the airship disintegrates and crashes into Metropolis, devastating the city in a massive explosion as the GUN forces and the heroes escape from the scenery.

Following this defeat, and with Dr. Eggman missing and presumed dead, the ruins of Metropolis were left to rust. The only visitors were those human scavengers brave or foolhardy enough to raid the ghost city for salvageable metals and technology, until more guests began to arrive.

In Chapter 5, Eggman provisioned Sonic with the necessary information to infiltrate the Metropolis Underground and stop the Marauders. The hedgehog arrived seconds too late, though; after expropriating the Master Emerald from its plinth, the Marauders abandoned the stronghold and returned to the Twilight Cage&mdash;leaving Knuckles' floating continent to crash square into the city.

In the end sequence of The Dark Brotherhood, the team return from the Twilight Cage to find Metropolis entirely rebuilt - and bristling with weaponry. Eggman promptly shoots the Cyclone out of the sky in something of a cliffhanger ending.

Sonic Forces
In Sonic Forces, Metropolis had become a pristine white city filled with advanced technolog. When Dr. Eggman began to successfully take over the world, Metropolis would explicitly feature its identity as Eggman's headquarters and capital central for the first time. Over the course of Eggman's six months of conquest, this mega city became the heart of the world-spanning Eggman Empire.

Upon discovering that Metropolis was left mostly unguarded, Knuckles lead the Resistance in an all out assault against the city in "Operation Big Wave". However Eggman's top commander, Infinite, countered the attack using the power of the Phantom Ruby to warp the gravity of Metropolis and create numerous large warped clones of himself. The resulting chaos caused the Resistance troops to panic and scatter, leading to at least 80% of troops being wiped out and forcing a tactical retreat. Despite this, a rookie member of the Resistance stayed behind in order to confront Infinite.

The two fought, the rookie initially proving no match for Eggman's commander, however after harnessing a mysterious gemstone the resistance member has discovered earlier, they were able to doge his vicious attacks. Although surprised by this, Infinite was unconcerned and decided to leave, noting that the entire Resistance would be wiped out in two days by his and Eggman's plan eitherway.

Believing they had destroyed the power source of Eggman's new power - the Phantom Ruby - by blowing up the Death Egg, the Resistance launched a second assault on the city. The Resistance's attack diverted Eggman's forces, allowing Sonic to head directly to Eggman's location. Upon reaching the doctor, it was revealed that the Phantom Ruby was still fully functional as the doctor had created a backup power source for the the gem under the imperial capital. Infinite then used the power of the Phantom Ruby to open a rift to Null Space - an allegedly inescapable void - to do away with the blue hedgehog once and for all. Sonic was sucked into Null Space alongside the rookie (who attempted to save Sonic from the Null Space). The two however were able to use their combined speed to escape the pocket dimension and made their way back to Eggman and Infinite's location. Baffled by this feat, the villainous duo retreated deeper into imperial territory to enact their final plan.

Sonic the Comic
In the Sonic the Comic series published by Fleetway Editions, Doctor Robotnik managed to conquer all of the planet Mobius and establish a totalitarian regime. While in power, he would rule the planet from Citadel Robotnik in the Metropolis City Zone after moving from the Special Zone's Egg Fortress.

Metropolis City was a focal point for many of Robotnik's traps and surprises for Sonic, including the infamous Hero of the Year Award and the ridiculous Mister Blobnik. Sonic and the gang visited the Zone quite frequently, attempting to disrupt Robotnik's rule there.

After the Doctor's regime was toppled in Issue #100, thanks to an electromagnetic pulse generated by Super Sonic,, the oppressed residents of Metropolis took back the city and razed Citadel Robotnik.

Archie Comics
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, the Metropolis Zone was initially a temporary location created by Eggman with the first Genesis Wave. In an attempt to stop Eggman's plans for Mobius, Sonic infiltrated the Metropolis Zone to stop Eggman once and for all. When Sonic found Eggman though, he began to realize what Eggman had done to the world, and after a brief battle, the hedgehog chased after Eggman to the Death Egg Mark 2.

As a result of the Super Genesis Wave, the Metropolis Zone became a permanent part of Sonic's World. In Sonic the Hedgehog #255, Sonic and Tails infiltrated the Metropolis Zone once more, this time to find and rescue Bunnie D'Coolette. When they found Bunnie, who was undercover in the Metropolis Egg Army, Sonic, Tails, and Bunnie fought their way out of the Zone.

Trivia

 * In Sonic Chronicles: The Dark Brotherhood, the map of Metropolis has a Sega Genesis, the Eggrobo from Sonic & Knuckles, the Drill Mobile from Marble Garden Zone of Sonic the Hedgehog 3, and the Capsule from the games from Sonic the Hedgehog 2 to Sonic & Knuckles.
 * The music for Metropolis in Sonic Chronicles: The Dark Brotherhood is a remix of Panic Puppet Zone Act 1's music from the Sega Saturn soundtrack of Sonic 3D Blast.
 * In Sonic the Hedgehog 2, the Metropolis was clearly located on West Side Island. In Sonic Chronicles: The Dark Brotherhood, it appears to be part of the same landmass as other locations in Sonic's world, implying that this version of the city is somewhere on South Island.