Pull the gate up in this defense game and make sure none of the attackers makes it through. You will be in charge of keeping the fortress secure as you are under siege from a race of barbarians. Use the cannon to shoot and hire units to fight.
In year 2222, people invented a portal. In year 2281, the first habitable planet is found. Its colonization is made through portals and it turns out that humans are not the only sentient race in the universe..