Caverns of Mars

Caverns of Mars is a vertically scrolling shooter for the Atari 8-bit family of home computers. It was programmed by Greg Christensen, with some features added by Richard Watts, and published by the Atari Program Exchange (APX) in 1981.[3] Caverns of Mars became the best selling APX title of all-time and was moved into Atari, Inc.'s official product line, first on diskette and later on cartridge.

Caverns of Mars
scan of the box cover art of the cartridge release
Box for the cartridge release
Publisher(s)Atari Program Exchange
Atari, Inc.
Designer(s)Greg Christensen
Programmer(s)Greg Christensen[3]
Richard Watts[4]
Platform(s)Atari 8-bit
ReleaseWinter 1981: APX[1]
April 1982: Atari (disk)[2]
1983: Atari (cartridge)
Genre(s)Scrolling shooter

The game is a vertically scrolling variation of Konami's 1981 arcade game Scramble. In Caverns of Mars, the player descends into cave and at the end must retrace their steps back to the top. Christensen wrote two less successful sequels, one of which scrolls horizontally and is very similar to Scramble.


Opening scene showing a fuel tank and static rockets

Caverns of Mars is a scrolling shooter similar in concept and visual style to the 1981 arcade game Scramble.[5] Christensen changed the orientation of the caverns from Scramble, having the player fly down into them as opposed to sideways through them. Unlike Scramble, rockets in Caverns of Mars remain on the ground.

Using a joystick, the player controls a ship descending into the tunnels of Mars, firing at targets along the way. The player's spacecraft has 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.


Greg Christensen, a high-school senior, purchased an Atari 800 in 1981, and created Caverns in "little more than a month and a half"—the first significant program he wrote in 6502 assembly language.[6] Fred Thorlin of Atari Program Exchange recalled Caverns arriving at APX:

It was received by APX in the morning mail. I saw it at 10:30. We showed it to the president of the company just after lunch. It was not a tough decision for him. Legal got in touch with Greg Christensen in short order. The young man, I think he was a community college freshman, suddenly had a bunch of money inflicted upon him. I was never certain whether he benefited from that in the long run or not.[7]

In the original version, when the player reaches the end of the selected map, the game ends. Thorlin felt it needed something more. Christensen was too busy, but agreed use his royalties to pay for someone else to do the work. Thorlin hired Richard Watts of Macrotronics to make a number of modifications. This included a new ending in which the player has to fly back out of the cavern in reverse before a timer runs out.[8]

Two months after sending it to APX, Christensen 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 in December 1982, Atari told Christensen he might receive up to $100,000 in royalties.[9]

Atari licensed the game in early 1982 for distribution in the main Atari catalog on diskette.[2] This was the first APX to Atari move, among very few examples in total. When asked to collaborate on a cartridge-based port, Christensen declined, having started college.[10] Atari released the cartridge version in 1983.[11][12]


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".[5] 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 takes advantage of a little-used mode allowing four colors per character.[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".[10] 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".[15] Electronic Fun gave it a 3.5 out of 5 rating, praising the action and pointing out only a few minor flaws.[16]

Caverns of Mars received a Certificate of Merit in the category of "Best Science Fiction/Fantasy Computer Game" at the 4th annual Arkie Awards,[17]: 32 


Mars Mission IIEdit

Christensen followed Caverns in 1981 with a lesser-known sequel, known originally as Caverns of Mars II. This version is very similar to Scramble, scrolling horizontally and with rockets that launch upwards from the ground. The game was completed in 1981, but it was not released. It would not be published until several years later by Antic Software as Mars Mission II.[18]


Combining the vertical orientation of the original Caverns with the improved graphics of Caverns II, Phobos was released through APX in 1982, although there are other minor modifications as well.[19][20] The levels are divided 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.

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".[21] 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".[15]


In 2005, a version of Caverns of Mars was included on the Atari Flashback 2 classic game console.[22]


Datamost's Cavern Creatures (1983) for the Apple II is very similar.[23] Conquest of Mars (2006) for the Atari 2600 is a direct clone.


  1. ^ APX Software Catalog. Atari Program Exchange. Winter 1981. p. 4.
  2. ^ a b "Caverns of Mars", The Atari Connection, Spring 1982, p. 11
  3. ^ a b Hague, James. "The Giant List of Classic Game Programmers".
  4. ^ Watts 2016.
  5. ^ a b Anderson, John J. (May–June 1982). "Atari Arcade". Computer Gaming World: 18.
  6. ^ "Caverns of Mars User's Guide" (PDF). Atari Mania. Atari, Inc.
  7. ^ Savetz, Kevin (April 2000). "Fred Thorlin: The Big Boss at Atari Program Exchange".
  8. ^ Watts 2016, 15:50.
  9. ^ Dale Archibald, "Programming for Dollars", Video Games, December 1982
  10. ^ a b "Caverns of Mars", The Creative Atari, 1983
  11. ^ Charlotte Thai, "Back to Basics", How they Got Game
  12. ^ Matt Barton and Bill Loguidice, "A History of Gaming Platforms: Atari 8-Bit Computers", Gamasutra
  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. ^ a b Stanton, Jeffrey; Wells, Robert P.; Rochowansky, Sandra; Mellid, Michael, eds. (1984). The Addison-Wesley Book of Atari Software. Addison-Wesley. pp. 89–90. ISBN 0-201-16454-X.
  16. ^ Gerson, Phil (April 1983). "Caverns of Mars" (PDF). Electronic Fun: 64. Archived from the original (PDF) on 2016-03-04.
  17. ^ Kunkel, Bill; Katz, Arnie (March 1983). "Arcade Alley: The Best Computer Games". Video. Reese Communications. 6 (12): 32–33. ISSN 0147-8907.
  18. ^ "Mars Mission II", Atarimania
  19. ^ "Phobos", Allgame
  20. ^ Keita Iida, "PHOBOS", Atari HQ
  21. ^ Bang, Derrick (May–Jun 1983). "Phobos". Computer Gaming World. p. 44. Retrieved 28 July 2014.
  22. ^ "Atari Flashback 2 specs", cnet
  23. ^ Shore, Howard A. (Jan–Feb 1984). "Cavern Creatures". Softline. pp. 49–50. Retrieved 29 July 2014.


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