Terni Lapilli

Boards for this game are scratched into paving all over the Roman world. Three pieces each, nine points, and — unlike tic-tac-toe — no way to fill the board and stop. When both sides have placed their three, play continues by sliding a piece to a neighbouring point, and it can go on indefinitely.

That is what makes it worth playing rather than merely solving. Tic-tac-toe runs out of moves; this does not, so a draw has to be agreed rather than reached.

RULES

• Each side has three pieces. Black goes first.
• Place all three of your pieces on empty points, taking turns.
• After that, a turn means sliding one of your pieces along a line to an adjacent empty point.
• Three of your pieces in a row wins — around the rim, or through the centre.
• A position repeated three times, with the same side to move, is a draw. So is a movement phase that runs 60 turns without a result.

CONTROLS

• Tap a point to place a piece; once your three are down, tap one of your pieces, then tap where it should go.
• Tap a selected piece again to change your mind.
• By keyboard: Tab to the board, arrow keys to travel round the points, Enter or Space to play the one you are on.