A Short History of Tic-Tac-Toe

Tic-tac-toe is one of the oldest known games, with direct ancestors in the Roman Empire and arguable precursors in ancient Egypt. Its modern form stabilized in Britain in the 19th century, and in 1952 it became the subject of one of the earliest video games — OXO, written for the EDSAC computer at the University of Cambridge.

Roman origins: terni lapilli

The clearest direct ancestor of tic-tac-toe is the Roman game terni lapilli (“three pebbles at a time”). Boards scratched into stone — typically a 3x3 grid or the older three-men’s-morris pattern — have been found carved into the pavements and walls of Rome itself. Archaeologists date many of these to the first century CE or earlier.

Three men’s morris

In medieval Europe the 3x3 grid was associated with three men’s morris, a close relative in which each player has three pieces that can be moved after placement. Three men’s morris is the small sibling of the more famous nine men’s morris and was widely played through the Middle Ages. The modern “no-movement” variant — our tic-tac-toe — is a simpler descendant of this tradition.

The name

The earliest recorded forms of the name are 19th-century British: tit-tat-to by 1818 and tick-tack-toe by 1869. In an 1884 print reference, “tick-tack-toe” described a different children’s slate game altogether — players would shut their eyes and try to bring a pencil down on one of a set of numbers on a slate. The name later transferred to the 3x3 alignment game in American usage.

The exact origin of the syllables is uncertain; the common folk explanation that “tick-tack” mimics the sound of a pencil on slate is not well supported. In the UK and much of the Commonwealth the game is still usually called noughts and crosses.

OXO (1952) — one of the first video games

In 1952 Alexander S. Douglas, a PhD candidate at Cambridge, implemented a full tic-tac-toe program called OXO on the EDSAC computer as a demonstration for his thesis on human-computer interaction. OXO played perfect tic-tac-toe against a human opponent, displayed the board on a cathode-ray tube, and accepted input via a rotary telephone dial.

OXO is widely cited as one of the first graphical computer games — predating “Tennis for Two” (1958) and “Spacewar!” (1962). It is historically significant because it proved a computer could play a nontrivial game perfectly, solving the game tree by exhaustive search.

Why tic-tac-toe is mathematically interesting

Tic-tac-toe is the simplest nontrivial “m, n, k-game” — the class of games where two players try to align k marks on an m×n board. With m = n = k = 3, the game is a solved forced draw. Enlarging the board or the alignment length leads to related games:

Related: Variants · Strategy · Glossary

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