In Troy, players play on a hex map of the area near Greece and Troy during the Trojan war. At the start of the game, each player draws a Decision Card at random, which is to be kept secret. The Decision Card determines whether they will assist Greece or Troy in their endeavor to win the war.
During a player's turn, in addition to trading and expanding as per the base game, they may attempt to put up to three resources face down into a "support row". Each donation will earn the player one trade token. When the support row grows to a sufficient size, a battle occurs. Of the five resources in the game, two award points to Greece while two others award points to Troy (the fifth resource does not contribute to either side). The side with the plurality of the resources wins the battle, and one victory point is awarded to the backers of the winning side (if the battle is a draw, no points are awarded). Victories awarded to Greece and Troy are kept on a scoring track on the board - players do not disclose which side they back until the end of the game.
Trade tokens may be used to build ships (which, unlike Catan: Seafarers are not road extensions out to sea, but instead are played in the middle of hexes). Each ship may be deployed from a coastal settlement or city, and give the player certain advantages, such as immediately awarding victory points, or allowing the player to take or replace cards from the support row once per turn. However, every time a ship is built or a 7 is rolled, a pirate is moved. The pirate, like the robber, may take resources from the owner of a coastal settlement or ship that is located at its new destination. If the pirate is moved to a space with a ship, the ship's owner may no longer use the privilege granted by the ship.
The game ends when any player has 15 victory points, or is leading when either Greece or Troy wins six battles. Trade tokens are used to resolve ties in victory points.
Read more about this topic: Catan Historical Scenarios II: Troy And Great Wall