Atlantis is a fixed screen shooter by Imagic, released in 1982.The player controls up to three (depending on difficulty settings) gun towers, used to destroy incoming enemy ships which attempt to destroy various parts of Atlantis, including the gun towers themselves. As enemy ships pass through the screen unharmed, they progressively make lower passes until they are at the lowest level, where they deploy a destructive energy beam.
In order to defend the city, the player has up to three cannons. The main cannon, positioned in the middle, shoots straight up and is fired by pressing the button by itself. Two support cannons are also available on either side of the screen. These cannons shoot at an angle and are fired by holding left or right on the joystick (depending on which gun you want to fire) and pressing the button.
After successfully defending each wave, the subsequent volley of ships comes a bit faster. Additionally, certain ships fly faster than others. Similar to Missile Command, lost structures and cannons can be regained at higher scores.
A very rare version of Atlantis called "Atlantis II" also exists. It was sent to the high-scorers of Imagic's "Defend Atlantis" contest in order to determine the final four finalists. This version is a faster and much more challenging version of the game.
Note that the ship that escapes the city once the player loses looks a lot like a ship from another Imagic game, called Cosmic Ark.
In the instructions to Cosmic Ark, the pilots of the mothership which is central to the game are even referred to as Atlanteans, suggesting that the game Atlantis takes place either before or after Cosmic Ark, or at least in the same creative universe.
The Intellivision version of this game had additional features, including spotlights used during the night raids, and a targeting reticule which more closely suggested the game play from Missile Command than the straight-shooting 2600 version of the defensive cannons did.