Reverse history in order to prevent Thessaloniki's siege in July 904 A.D. by Leo of Tripoli and his Saracen pirate fleet, by solving a range of brain-teasers, riddles and code-breaking. A game created and implemented by Gamecrafte creative team. The game master (GM) explains the situation to the participants: we are in Thessaloniki of 904 A.D. and we are aware that the notorious Leo of Tripoli and his Saracen pirate fleet are heading towards Thessaloniki. The sea walls are the city's weak spot of defense. Byzantines renovate them, but they still are not sufficiently high and strong to prevent the siege. Then the GM presents gradually the challenges to be solved, in order to save the city: code-breaking, riddles and other brain-teasers. The activity lasts 1 1/2 hours approximately. It takes place at Ticking Clock's events venue at the western edge of the city's centre.