You start the game with four Short Swordsmen, four Composite Bowmen, four Horse Archers, and six Cavalry. The first part of the mission involves reaching the Heavy Transports, which will take you to your reinforcements. Go north along the edge of the map, defeating the units in your way, until you reach the enemy towers. Go past them (don't try to destroy them, it'll cost you more troops than just walking past) and head south-west, until you reach the shore. Once the units are dead, destroy the towers with your Stone Throwers, and capture the Artifact so you can ship it back to your island.