During exploration, minor tribes that have not yet advanced to be civilizations may be discovered in the world. These are represented by a small hut symbol. If you enter a minor tribe’s village by moving onto the hut, one of a number of things may happen: you may discover valuable metals (coins), the tribe may become a mercenary unit in your army, you may discover a scroll of ancient wisdom that advances your civilization, your magnificence may inspire them to become civilized and found a new city in your empire, or they may prove to be extremely violent barbarians. - Manual
Only ground units of civilizations (the player or AI) are eligible otherwise with air units or barbarians, nothing will come of minor tribes and it simply disappears.
- You have discovered valuable metal deposits worth 50
- You have discovered scrolls of ancient wisdom
- You have discovered a friendly tribe of skilled mercenaries
- You have discovered an advanced tribe
- The square needs to be deemed suitable enough for a city by the game's logic. Sites that are lacking in food production for potential city sites do not become cities.
- You have unleashed a horde of barbarians!
- The size of the horde is determined by the total number of cities by the player.