Tower Defense Games

Tower Defense Games or TD Games are essentially a sub-genre of strategy games. The TD Game genre is generally comprised of a human player who allocates resources to build 'Towers' in order to prevent enemies (commonly referred to as 'creeps') from passing through the human players map. In order to succeed in the TD Game genre, human players have to allocate resources in order to build defensive towers. These towers have the ability to shoot, damage, halt, and eliminate creeps from the map. Each eliminated creep results in gained resources, these resources are then stockpiled by the human player to buy more towers, or upgrade current ones. Winning is usually defined as surviving the onslaught of creeps (The human's towers eliminate all (or a sizable portion) of the creeps) and losing is defined as the creeps reaching the end of the map before your towers have a chance to take them out. TD Games are usually very easy to pick up however hard to master.

TD Games can be simple or complex, turn-based or real-time and they all involve some sort of strategic approach.

Elements

Phillipa Avery describes the 5 elements that combine to comprise an example of the TD Game in his text, "Computational Intellegence and Tower Defense Games".

Terrain

The map. Users can strategically place their towers on any part of the map. This map is usually comprised of two elements, the path and the area surrounding the path. Creeps travel along the path through the map. Towers can be placed anywhere on the terrain that is not on the path. Maps can change through different levels.

Towers

Towers are the human player's defense against the invading creeps. Normally towers can be placed anywhere on the map except directly on the path. Towers can be upgraded with resources. Towers have many different abilities, costs, and uses. They cover different ranges and have specific targets. Towers can differ in cost, range, power, firing rate, effect on creeps and more.

Creeps

Creeps are defined as the enemy. Creeps move along the path at varying speeds trying to reach the end of the path. Creeps usually have different attributes such as size, speed and defense. Usually in TD Games, the creeps that follow the path in the beginning levels are relatively low strength and low speed. As your progress through the game, these creeps increase in armor, speed and size and typically take multiple upgraded towers to kill. Some creeps are unaffected by certain towers, thus the human player is best served to diversify his arsenal of towers.

Reward Systems

These reward systems are created to, as Avery states, "...increase the interest and lengevity of TD games..." As the creeps pass though the map, the towers destroy them. As each creep is destroyed, typically, the human player is rewarded with some sort of resource. These resources can be used to purchase tower upgrades, new towers, and more. These resources function as a way for the users to increase the power of their tower defense in order to sufficiently withstand the next levels creeps.

Single or Multi-player

The majority of TD games involve a singe player strategizing the use of his tower defense against the computer-controlled creeps. However there are examples of multi-player TD games such as Rampart as well as others that function to have humans work as a team to withhold the onslaught of creeps.

History

Early Beginnings

The Tower Defense Game genre is relatively young in the world of gaming. The TD Game genre finds its beginnings in 1990, with an arcade game released by Atari Games titled Rampart. The large success of Rampart caused the game to be released on a wide variety of platforms including Game Boy, Super NES, Playstation, Xbox, and more.

Increase in Popularity

The success of the Tower Defense model generated significant buzz in the gaming community and eventually influenced the creation of custom maps that adopted the TD Game Model for mainstream computer games such as Starcraft, Age of Empires II, and Warcraft III. Fans utilized the free map creation tools in Starcraft and Warcraft III to create custom TD style maps. These Tower Defense maps became so popular that the game developers themselves included TD style levels in further releases of the game as well as in expansion packs. As noted in Phillipa Avery's text, Computational Intelligence and Tower Defence Games, "One of the most popular versions of these [tower defense model-based maps], and arguably the original true TD style game was the Tower Defense maps for the Warcraft III expansion The Frozen Throne." This addition in the Warcraft III expansion signaled the TD Game genre's entrance into the mainstream and sparked a growth in the genre's awareness on a larger level.

Entrance into the Mainstream Market

The Tower Defense Game genre entered the mainstream market with the boom of flash-based web games. Until 2006, no one really bothered to develop a desktop-based model of the Tower Defense Game. In early 2007, a developer named David Scott launched Flash Element Tower Defense. This game was so successful that within two days, 500,000 users were playing it per day. The success that David Scott achieved with Flash Element TD rubbed off onto one of Scott's close friends, Paul Preece. Preece released Desktop Tower Defense in March of 2007 and within 4 months the game had been played over 15 million times and brought in over $12,000 in revenues. Desktop Tower Defense soared in popularity, garnering awards such as the 2008 Gleemax Award for Strategic Gameplay (“The Gleemie”) at the Independent Games Festival and it's success is credited with the launching of the Tower Defense Game genre into the mainstream.