Narrows

Narrows is a multiplayer map exclusive to Halo 3, and may be a remake of Gephyrophobia.

Discovery
It was first discovered in the third Bungie Podcast of Summer 2007, and was listed as having a "Very special weapon in the middle". It was further detailed in a Bungie Humpday Challenge as a long Forerunner outpost set in a snowy and cold environment, and was revealed to be the external bridge level featured in one of the Halo 3 video documentaries. It was known by the codename "Chill" during Spring 2007, and was discovered in the hexadecimal code of the Halo 3 Beta. It was later relabeled as "Long and Lean". It stayed that way for a long time, until suddenly, Bungie released pictures of the map, calling it "Narrows".

Layout
"Narrows", is a fully symmetrical map, with two opposing bases on each end connected by a Forerunner Causeway. The weapons in each base are identical, with a few minor changes. A Man Cannon, exists on one side of each base, and propels the player to the opposing base on the other side of the canyon. If players are to enter opposing man cannons at roughly, the same time they will collide in mid-air and both fall to their death. The main bridge, features two different levels for players to combat each other. The upper level is vaster, allowing players to be hit from multiple sides and angles. The lower level, connected by a "lean" Energy Bridge is more discrete, and often less hazardous. This map resembles the bridges in the Halo: CE levels, Assault on the Control Room, and Two Betrayals.

Base Spawns
Each team spawns, at opposite sides of the map, and must cross the bridge or jump through the Man Cannon to engage the enemy team. The two bases have been nicknamed "Blue Base," and "Yellow Base" by players, due to the blue and yellow tinting of each base. From Blue Base, players can access the Man Cannon to their right, while Yellow Base players will find the Man Cannon, to their left.

Each base features identical weapon spawns and placement. The main differences in each base are due to aesthetics, equipment, and power-ups. Yellow Base players have a Power Drain placed in front of their Man Cannon, and Blue Base players have a Bubble Shield. Each base features a low point, which is even lower than the "Low Bridge." Blue Base players have an Overshield power-up available, and Yellow Base primarily had Active Camouflage, though replaced with an overshield in an update. In addition, this low point contains a Brute Shot (available on each side).

Upper Bridge
This bridge connects the two bases, and is generally the area where most of the fighting occurs. The upper bridge features a lot of open areas and not a lot of room for cover. The M41 Rocket Launcher used to be found at the center of this level, but this is now replaced by a Bubble Shield. Separated from the top, but accessible via ramps on the four corners of the bridge, you can find the lower bridge.

Lower Bridge
This lower bridge offers more protection than the upper level. A Rocket Launcher replaces the Shotgun spawn, in the center of the Energy Bridge, which connects the two bases. Players can also find the SRS99D-S2 AM Sniper Rifle on each side of the bridge. Taking the lower bridge may be a safer and quicker route to each base, but can leave the player vulnerable to rocket or sniper fire. It is also possible to fall off the bridge and land on the cooling core below. You can not stay here for long though, as you will kill yourself after 5 seconds, or the "kill" will go to the Guardians. Careful players can jump down onto a covered ledge and hide on this cooling core without dying, but most players will agree this is not an honest strategy.

Inspiration
The map's design is similar to the outdoors bridges on the Halo: Combat Evolved campaign levels Assault on the Control Room, Two Betrayals and the multiplayer map Gephyrophobia, although Gephyrophobia was noticeably bigger. It also seems to borrow elements from the Halo: CE map, Longest.

Strategies

 * In Capture The Flag games, players can actually "throw" the flags with the man cannons and stay behind to defend The Man Cannons. This can be especially helpful because the cannons "throw" the flag very close to a players return point.
 * At the start of the game, Rockets should be top priority; at least two people should go straight for them. If one dies, the other can hopefully take them.
 * At the beginning of the game, there would normally be a Sniper shootout at the Sniper spawns, a second player on your team can take advantage of this and not only help their Sniper with a Battle Rifle, but also take the Rocket Launcher in the fray.
 * The Man Cannons are the quickest way across the map, people will use these often to catch you off guard, make sure someone keeps an eye on them. Use these with caution, when you are fired through the cannon a very distinguishable sound can be heard across the map and all eyes turn to the cannons and the arcing path that connects them and the bullets will fly. If you are targeting anyone on their way across the arc, using a battle rifle is extremely effective. The easiest way to kill someone using the man cannons is to be at the receiving end of somebodies transit. As they get closer and closer you will be able to land a lot of shots on the incoming enemy. If you are the enemy in transit it is surprisingly difficult to hit targets waiting for you at the end so be sure to check your landing zone with a scoped weapon to make sure you aren't setting yourself up for an ambush.
 * Shooting across the Man Cannon at the beginning of a Team Slayer match will allow you to take out the opposing sniper, who is probably focused somewhere across the map. (http://www.halogopro.com/narrows.html )
 * The Power-ups are under the Sniper Spawn, remember they can be useful against the Sniper or the Rocket user on the other team. Overshield is more practical against the Rockets, in case they notice you, and invisibility against the Sniper, because they will often be in scope, no motion sensor or target to see.
 * As a Sniper, a good place to be sniping would be right at the back in the centre, where you can see your half of the bridge at a distance, and go for a view on the man cannon. Also a good sniper space is just to the left and right of the start of each side of the bridge is a raised walkway that can put you high up to see the entire bridge and you cannot be sneak attacked from behind while in zoom view.
 * If you jump on the boundaries on the far ends of the upper level of the bridge, you can leap to the bottom levels of the respective bases. This makes for a quicker route to the flag or bomb return points, or in death match a quick getaway.
 * Right next to your flag spawn, opposite of the wall, a little bit before the explosive barrels, is small little ledge against the pillar that you can go up a few feet and be concealed from most viewpoints. It's a good place to camp with Mauler when guarding your flag or to hide when you have the lead in a Team Doubles game, for there is a little ledge on both bases in the exact same point, so they are opposite of each other.
 * While flying from one of the man cannons, or jumps. it is worth trying to grenade enemy players on the bridge as you pass in hopes of getting a kill and/or softening them up for your team-mates.
 * If you collide with an enemy player in midair from the jumps, try to melee them, because your enemy will fall and you can get the point for killing them if it is a slayer gametype.
 * Beware of the new spawn system. Your opponents often spawn behind you.
 * Although the map seems very small, it would be smart to get a sniper rifle at the beginning of the match.

Forge

 * In monitor mode, you can get off the main bridge and go to a small "outcropping" ledge in the canyon wall, the space is large enough to forge on, and have players fight there. The only way to have players reach it is to place a receiver node on the ledge, and a sender node on the main bridge.
 * Forging boxes to help jump onto the little towers can help on a game of snipers.

Matchmaking Adjustments
For reasons not yet disclosed by Bungie, this map has been slightly altered when playing in Matchmaking playlists.

As of the December 11, 2007 update, two of the Maulers that spawned along the top of the bridge (one on each side) have been removed. The remaining Mauler on each side was re-positioned centrally and slightly back from the original locations, behind a wall offering cover from the M41 Rocket Launcher spawn location. In addition, the Radar Jammer has also been removed, though this happened in an earlier Matchmaking update.

It is believed that this change was caused by near-constant complaints regarding the large number of Maulers in many levels combined with the Mauler's ability to nearly-instantly kill an opponent at very close range. Many people felt that the weapon was unbalanced because of the close-quarters power of the Mauler, especially in CQB-style levels; this is a misconception.

As of August 22, 2008, the Shotgun and the Active camo were also removed and as of the M41 Rocket Launcher, it has been moved to the location where the M90 Shotgun was. The Bubble Shield is now on the top where the Rocket Launcher was, and there are two Overshields in the same location.

Trivia

 * It is possible to get outside the map. In Forge, you can place teleporters on top of Narrows. You can't jump because you are too high. If you go too far forward, you won't be able to go back.
 * It is possible to survive for a brief period of time on the lower structure. After a undetermined period of time you will be killed by the guardians. This is because the game is processing the fact that there is no way you can get back up, and so it kills you. However if you crouch one of the holes along the outside, you will be able to survive until you are killed by another player (or, of course, yourself by committing suicide).
 * If you look off to the side, you can see another bridge exactly like Narrows. That bridge and this one (Narrows) are probably part of an extremely large cooling installation, as said in the description of the map.
 * If two people go on the Man cannon (one on each side) and launch at the same time, they will hit each other and thus fall to their deaths.
 * On the conveyor-belt there are crates and turret cases that the UNSC uses.
 * The 'conveyor belt' is actually a large water mill, which brings the chilly water from beneath the level to an as of yet unknown place where it is used for cooling down the Ark.
 * In Forge, you can overload the man cannons with Trip Mines. If you do this, you can simply stand on them with no effect.
 * If you overload the map, the Man-Cannons will seem to still be working, though they in fact are not.
 * While going over the Man cannon if a player throws out a Regenerator, the player will then go back to where they come from, usually falling to their death.
 * Although the map description says that it is set on the Ark, no other part of the Ark can be seen in the sky. This is most likely because the mountains and clouds block any view of the Ark. Also, the Ark's artificial sun can be seen in the sky.
 * The early version of Narrows' structures seem to be black in colour, compared to the greyish-brown of the final version of the map.
 * There are tons of hiding spots on the map. As seen by this video http://www.youtube.com/watch?v=MODhfbmzuVI