Tower Defense

Tower defense is a game type, common to certain subsects of the real-time strategy genre, whereby players create units or towers in order to stop non-player controlled enemies from reaching a certain goal point. A typical "Tower Defense" game would consist of a flat playing field, with clearly marked, distinct pathways which the non-player controlled enemies follow to reach the goal. Enemy units are created at set intervals at a set starting point; they then travel along the marked pathways towards the goal point. Typically, enemy units are divided up into "waves". Each wave consists of the same type of unit, though unit combination waves may also exist. Players build towers alongside or on (but never blocking) the pathways, attempting to destroy the enemy units that pass by. Each subsequent wave has tougher or faster units, so players must continue to build or upgrade to new units and towers or risk being overrun. There are a finite number of waves, usually around 40-80, depending on the specific scenario, and if all the waves are destroyed then the players win. If enough enemy units make it to the goal point (this number also varies per scenario), then the players lose.

This entry is only a general outline of Tower Defense, which can be exceedingly complicated in all its intracicies. Making generalizations about Tower Defense is a practice also fraught with danger, due to the extreme mutlitude of different Tower Defense scenarios currently in existence. However, certain strategic and tactical properties still remain inherent across all Tower Defense game types. Players start with a sole worker, that then use to build different types of towers. They have limited resources, so they have to pick and choose what type of towers to build, and where to build them. Corners, where the pathway enemy units take turns, are often the most lucrative areas to erect tower fortifications. If players are allowed to build on the pathway itself (to construct their own pathways for the waves, in other words), a practice called "mazing," they should try to snake their towers back and forth, in order to maximize the time enemy units spend in the maze. One must destroy enemy units, in order to collect their resource bounties, but one must also work with other players to take down the waves, for no one player can win Tower Defense by himself. Upgrading to new and better towers, or new and better units, is necessary to defeat the waves as they grow stronger and your towers get relatively weaker.

An interesting variation on Tower Defense involves a scenario where enemy units focus on a single player-controlled unit, trying to destroy it. This unit is typically quite powerful. Other players build towers to protect the unit. If it dies, the players lose. Enemy units also spawn in waves. Other variations include enemy waves being able to attack the player towers (in regular Tower Defense they do not), players spawning their own waves in order to destroy other players (instead of playing against a non-player controlled entity, players in this game type play against each other), and players fighting against both non-player controlled enemy waves and each other at the same time.

Tower Defense game types are extremely popular "custom" maps in Age of Empires II, StarCraft, and Warcraft III, apart from the regular game. "Photon Defense" is the archetypal Tower Defense map for StarCraft; Warcraft III has "Wintermaul" and "Azure Tower Defense." The variations, of course, are endless.