Bugs

The story goes like this. In the original Civilization, released by MicroProse in 1991, every leader is assigned a numerical aggression value. Mahatma Gandhi is given the lowest possible aggression: 1, on a scale where most leaders sit between 4 and 7. When a civilization adopts democracy as its government, the game subtracts 2 from its leader's aggression. Gandhi's value, the story says, drops to -1. The variable is an unsigned 8-bit integer. -1 wraps around to 255, the highest possible aggression value in the system. Pacifist Gandhi suddenly becomes the most warlike leader in the game and starts firing nuclear weapons at his neighbors.

The story is told everywhere. It is on Wikipedia. It is in Hacker News comments. It is in textbook chapters on integer overflow. It is in a thousand programmer conversations as the canonical example of why type discipline matters.

The story is almost certainly not true.

Sid Meier, the lead designer of Civilization, addressed it directly in his 2020 memoir. The original game's aggression values were stored as signed integers in C, not unsigned. A negative value would have remained a negative value. The behavior the story describes could not have occurred in the original code. Brian Reynolds, lead designer on Civilization II, has gone further: he reviewed the source code from memory and stated that no part of the aggression logic could have produced a maximum-aggression Gandhi by underflow.

The actual nuclear Gandhi exists in Civilization V, released in 2010. The Civilization V designers, aware of the popular myth, deliberately wrote Gandhi's nuclear-launch threshold lower than other leaders', as an inside joke. Gandhi in Civilization V is statistically more eager to use atomic weapons than any other leader in the game. The bug had never existed; the joke implementation made the bug retroactively real.

The story is included in this guide because of the form it takes, not the fact it claims. An anecdote about a bug is socially much cheaper to repeat than the bug itself, which would require a debugger. Once a bug story is good enough to remember, the question of whether it actually happened becomes a curiosity for historians and irrelevant to programmers, who will tell the story anyway.

The nuclear Gandhi myth is now closer to truth than it has ever been, because Firaxis put it into the game. The original bug, if there ever was one, is unfalsifiable: the 1991 codebase is not public, and the engineers who wrote it say it did not happen. The specimen pinned to this page is a story about the bug, not the bug.

The lesson, such as it is: not every famous bug is a real bug. Some bugs are good enough as stories that the industry has agreed to remember them anyway.