Fortress is a two player abstract strategy game where players take turns placing stones at intersections on an 11x11 grid board. Players try to both capture their opponent’s stones and also to create fortresses to score points.

The game also comes with rules to play an advanced version of Tic-Tac-Toe using the same playing pieces and board.

From the box:
“Fortress is a simple game of mysterious Oriental flavor. A player tries to organize large but defensible fortresses. His opponent must exploit its weakness and mount an earnest attack. At the end, the winner is declared, based on the number of prisoners and size of its fortresses' territory.”