Caverns of Mars

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Caverns of Mars
Screenshot of Caverns of Mars

Developer(s) Greg Christensen
Publisher(s) Atari Program Exchange
Designer(s) Greg Christensen
Engine Assembler
Platform(s) Atari 8-bit
Release date(s) 1981, 1982, 1983
Genre(s) scrolling shooter
Mode(s) single player

Caverns of Mars is a computer game for the Atari 8-bit computers, programmed by Greg Christensen and published by Atari Program Exchange (APX) in 1981. It became the best selling APX title of all time, eventually being released by Atari in cartridge format.


High-school senior Greg Christensen, purchased an Atari 800 in 1981, and wrote Caverns over a six-month period. Two months after sending it to Atari Program Exchange (APX) he received his first royalty check for $18,000, and a phone call from an Atari executive who praised the game. Caverns eventually won the 1981 APX game contest, winning another $3,000, and as of December 1982 Atari told Christensen he might receive up to $100,000 in royalties.[1] Atari licensed the game in early 1982 for distribution in the main Atari catalog, distributing it on diskette.[2] This was the first such example of an APX to Atari move, among very few examples in total. When asked to collaborate on a cartridge-based port, Christensen declined, having started college.[3]


Opening scene in the original Caverns of Mars. The rockets are unmoving.

Caverns of Mars is a vertically scrolling shoot 'em up similar in concept and visual style to the 1981 arcade game Scramble.[4] Christensen changed the orientation of the caverns from Scramble, having the player fly down into them as opposed to sideways through them. For technical reasons, vertical scrolling is somewhat easier to implement on the Atari platform. Unlike Scramble, the targets generally did not move relative to the map.

Using a joystick, the player controls a ship descending into the tunnels of Mars, firing at targets along the way. The player's spacecraft features two cannons, positioned on either side of the craft, firing downwards. The player needs to avoid hitting the cavern walls, while shooting targets of opportunity along the way. Fuel tanks can be shot to add 5 points of fuel, and the craft is destroyed if it runs out.

There are several different sections of the map, with easier skill levels removing the more difficult sections from the areas through which the player has to fly. The easiest skill level has only three sections, the hardest has six. On any skill level the last section of the map is a reactor, which the player lands on and thereby sets to explode. The player then has to reverse course and fly up and out of the caverns to escape before the reactor explodes.

Sequels and re-releases[edit]

Early scene in Caverns of Mars II, a side-scroller now almost identical to Scramble.

Christensen followed Caverns in 1981 with a lesser-known sequel, known originally as Caverns of Mars II. The game was completed in 1981, but not published until several years later by Antic Software as Mars Mission II. This version was more similar to Scramble, including rockets that launched upwards from the ground. In the original Caverns they were static objects.[5]

Opening in Phobos, showing the improved "Scramble-like" graphics.

Effectively a version of the original Caverns with improved graphics, Phobos was released through APX in 1982, although there were other minor modifications as well. Gameplay was vertical as in the original.[6][7] The levels were broken down into sub-levels with letters as names; after being killed the action restarts at the top of the sub-level, as opposed to the top of the whole level. The system is similar to the one used in Moon Patrol.

In 1983, Atari released Caverns of Mars on a cartridge (RX8021) as an official Atari product, one of the few user-submitted programs to ever become an official Atari product.[8][9]

In 2005, a version of Caverns of Mars was included on the Atari Flashback 2 classic game console.[10]

Opening level in Conquest of Mars on the Atari 2600.

In 2006 a homebrew version of the original Caverns of Mars, titled Conquest of Mars, was released in cartridge form via AtariAge for the Atari 2600 system.[11] Christensen was not involved in this project.


Computer Gaming World called Caverns of Mars "delightful ... addictive and excellently paced". It noted the age of the author and stated that the game "has all the look, feel, and play of a 'professional' program".[12] Softline liked the game's use of checkpoints after losing a life, and concluded "This game is great; you'll find it difficult to pull yourself away".[13] Compute! called Caverns of Mars‍ '​s graphics "impressive … an excellent use of the Atari's graphics capabilities", noting that the game used the rarely used four-color mode.[14] A Creative Computing reviewer opened with "Four minutes later. I was hooked. Four hours later, my wife dragged me away." and concluded by noting that "The Caverns of Mars has that indefinable "something" that makes it arcade-quality".[3] The game received a Certificate of Merit in the category of "Best Science Fiction/Fantasy Computer Game" at the 4th annual Arkie Awards,[15]:32 and The Addison-Wesley Book of Atari Software 1984 gave the game an overall B+ rating, calling it "fast-paced and addictive" and "great fun ... a must for any dedicated arcade game player".[16]

Softline stated that Phobos might disappoint Caverns of Mars players, stating that it was "a reinvention of the wheel" and too easy for them. The magazine noted some improvements, such as a pause button and multiple skill levels, but advised that "Mars veterans should wait".[17] The Addition-Wesley Book of Atari Software 1984 gave the game an overall B rating, stating that "whether it is a better game than the original is debatable" and concluding that "it is a good choice for the dedicated arcade game player".[16]


  1. ^ Dale Archibald, "Programming for Dollars", Video Games, December 1982
  2. ^ "Caverns of Mars", The Atari Connection, Spring 1982, p. 11
  3. ^ a b "Caverns of Mars", The Creative Atari, 1983
  4. ^ Overview of Caverns of Mars at
  5. ^ "Mars Mission II", Atarimania
  6. ^ "Phobos", Allgame
  7. ^ Keita Iida, "PHOBOS", Atari HQ
  8. ^ Charlotte Thai, "Back to Basics", How they Got Game
  9. ^ Matt Barton and Bill Loguidice, "A History of Gaming Platforms: Atari 8-Bit Computers", Gamasutra
  10. ^ "Atari Flashback 2 specs", cnet
  11. ^ "Conquest of Mars (Champ Games 2006)", The Basement Arcade, 15 November 2007
  12. ^ Anderson, John J. (May–June 1982). "Atari Arcade". Computer Gaming World. p. 18. 
  13. ^ Bang, Derrick (May 1982). "Caverns of Mars". Softline. pp. 14–15. Retrieved 15 July 2014. 
  14. ^ Brannan, Charles (July 1982). "Caverns of Mars". Compute! (review). p. 183. Retrieved 30 October 2013. 
  15. ^ Kunkel, Bill; Katz, Arnie (March 1983). "Arcade Alley: The Best Computer Games". Video (Reese Communications) 6 (12): 32–33. ISSN 0147-8907. 
  16. ^ a b Stanton, Jeffrey; Wells, Robert P. Ph.D.; Rochowansky, Sandra; Mellid, Michael Ph.D., ed. (1984). The Addison-Wesley Book of Atari Software. Addison-Wesley. pp. 89–90. ISBN 0-201-16454-X. 
  17. ^ Bang, Derrick (May–Jun 1983). "Phobos". Computer Gaming World. p. 44. Retrieved 28 July 2014. 

External links[edit]