Tap the game to open it fullscreen. On a computer, Esc exits; on a phone, use the ✕ button.

How to play

A cross of stakes spins over the site. Tap (or press the space bar) when it lines up with the golden plan cross. There are four stages, one per quarter of the fortress; at each stage the spin speeds up and the tolerance shrinks. Three mistakes end the game.

The story behind it

Trelleborg was raised around 981, with four gates and sixteen longhouses inside the ring. The game simplifies the work into four stages. Read the story in Trelleborg: the circular fortress the Vikings built with perfect geometry.