Rules of Hnefatafl:

1. Black moves first.
2. Black's objective is to surround the white king on all four sides, or on three sides plus the central square (the throne).
3. White's objective is for the king to escape to a corner square.
4. The king cannot be captured along the edge of the board.
5. Capturing is via custodial capture: a piece is captured if it is sandwiched between two enemy pieces, but only if it is sandwiches as a result of an enemy move --- ie. you can move a piece between two enemy pieces, and your piece is not captured as a result.
6. The corner squares are hostile to black for the purpose of capturing.
7. The throne is always hostile to black, but hostile to white only when unoccupied.
8. A player with no valid moves loses the game.