Heroes of Gaia (Chinese: 英雄之城; pinyin: Yīngxióng Zhī Chéng), known in the separate European version as Castle of Heroes, is a massively multiplayer online fantasy browser-based strategy game developed by the Chinese developer Snail Games and published in the United States by its U.S. publishing division, Snail Games USA.

Players start with a small but varied complement of troops and a blue quality Hero to command them.

5 resources are needed to construct buildings and recruit troops: Gold, Lumber, Ore, Sulphur and Crystal.

Heroes can be equipped with items to increase their stats and with spells to use in combat to aid their troops.

60-80% of the units lost in combat will appear in the player's Infirmary (located in the Arena building) and can be revived for a quantity of Gold.

Some players strive to have the highest individual Fame on the server, others try to have the most impressive army or be the one to have defeated the most enemy troops.

Some other players work to get a Hero and army strong enough to beat the Babel tower.

For a lot of players, the goal is to elevate their guild to prominence in the rankings and control the most Capital Cities.

Each battle fought awards the Hero experience and every 10th level will reward the player a powerful piece of equipment.

2009 Heroes of Gaia received the Jing Ling award[5] for being "the best Webgame" in China.