Pessoi is a playable reconstruction of the ancient Greek game later called petteia or polis — the strategy game Plato and Aristotle reached for when they wanted an image of being outthought. It is older than chess, and it is nothing like it: no royal piece, no checkmate, no back-rank army. You surround a piece to take it, and you win by hemming your opponent in until they have no move at all.
πεσσοῖσι προπάροιθε θυράων θυμὸν ἔτερπον “… at pessoi, before the gates, they delighted their hearts.” — Homer, Odyssey 1.107, the game's oldest witness
Every piece is equal — “dogs,” two colours, no king. You win by blockade: leave your opponent unable to make a single legal move.
Flank an enemy piece on two opposite sides with your own and it is removed. The game Pollux called taking a piece “by enclosing it between two.”
Rebuilt from the ancient evidence — Homer to Pollux — not borrowed from a modern rulebook. A 7×7 board, deliberately neither chess's 8×8 nor a Go grid.
Four ideas, none of them borrowed from chess. A full game takes a few minutes; the rules panel lets you toggle the historical variants.
Take turns dropping your pieces onto any empty cell. No captures while you set up.
A piece slides like a rook — any distance along a rank or file, through open ground.
Close a piece between two of yours on opposite sides and it falls. Moving into a gap is safe.
Leave your opponent with no legal move and you win — the cornering of Plato, the noose of Polybius.
No complete rulebook survives, so every rule is graded by how well the ancient sources support it — A attested I inferred D design — and the genuinely open choices were settled by a tested engine and self-play, not by assertion.
Homer · Plato Republic, Phaedrus · Aristotle Politics · Polybius 1.84 · Pollux Onomasticon IX.98 — the Greek game
Ovid · Martial · Laus Pisonis · Isidore XVIII.67 — the Roman reception (ludus latrunculorum)