The object of the game is to prevent the waves of monsters from getting to the castle by building element towers near the path. Your menu is located at the bottom of your screen. You can choose from a number of different elements to build towers from. When you click on a tower that has been built, the build menu becomes an upgrade menu, allowing you to make your towers stronger. The monsters will spawn every 20 seconds. Their health will be multiplied by 1.25 with every wave. If your towers fail to kill the monsters, and they do get to the castle, a civilian of your castle will die. When all of your civilians die, the game is over. Best Tower Defence games.