Three in a row. It might be the oldest game idea humanity has. Boards for three-in-a-row games have been found scratched into roofing slabs in ancient Egypt and carved into the stone steps of Roman buildings. Whatever else changes, people apparently cannot resist lining things up.
The rules in 60 seconds
- The board is a 3×3 grid. One player is X, the other is O. X traditionally moves first.
- Players take turns claiming one empty square each turn.
- The first player to get three of their marks in a straight line — across, down, or diagonally — wins.
- If all nine squares fill with no line completed, the game is a draw (a "cat's game", in playground slang).
That's the whole game — which is exactly why it has survived three millennia and why it fits on the back of a napkin, a chalkboard, or a phone screen.
Where it came from
The direct ancestors of tic tac toe are hard to pin down, because three-in-a-row games appeared independently all over the ancient world. The Roman game terni lapilli ("three pebbles at a time") used the same grid, though players had only three pieces each and moved them around rather than adding new marks — closer to what we now call Three Men's Morris. Grids for it are still visible carved into pavement stones across the former empire.
The modern pencil-and-paper form — where marks are written and never move — solidified in 19th-century Britain under the name noughts and crosses ("nought" being an old word for zero). The American name "tick-tack-toe" originally referred to a completely different children's game of tapping a slate blindly with a pencil to score points; the name migrated to the grid game in the 20th century and stuck.
A footnote in computer history
Tic tac toe also has a serious claim to fame: it was one of the first video games ever made. In 1952, Alexander (Sandy) Douglas at the University of Cambridge wrote OXO, a noughts-and-crosses program for the EDSAC computer, as part of his PhD on human–computer interaction. A game so simple a child masters it was, fittingly, the first game a computer did too. It has been a standard first project for programming students ever since — and a standard demonstration in game theory, because the full game tree is small enough to draw by hand.
Why every game ends in a draw (between experts)
Tic tac toe is what mathematicians call a solved game: every possible position has been analysed, and with best play from both sides the result is always a draw. There are 255,168 possible distinct games, but only a handful of decisions that actually matter — which is why a bit of study makes you effectively unbeatable. (We wrote a full strategy guide if you want to be the person who never loses.)
Variants worth playing
- Bigger boards. On RivalPit you can stretch the grid from 3×3 up to 10×10 and set the winning line to 3, 4, or 5. The game stops being a solved draw and becomes a genuine fight for space — closer to Gomoku, its five-in-a-row cousin.
- Most-lines scoring. Instead of ending at the first line, the board fills completely and every completed line scores a point. Suddenly every square matters to the very end.
- Three Men's Morris. The ancient movement version: three pieces each, and after placing them you slide pieces to adjacent squares trying to line them up.
- Misère tic tac toe. The inverted game: whoever makes three in a row loses. Harder than it sounds — the center becomes poison.
Why it endures
Tic tac toe survives because it is the perfect first strategy game. It teaches looking ahead, spotting threats, and thinking about what your opponent wants — the exact mental muscles every deeper game uses — in rounds that last thirty seconds. It's a doorway. And on a rainy afternoon, best-of-eleven against someone you love beating, it's still just fun.