The travelers are units that sometimes take camp next to your city. They can prove themeselves to be quite useful at times and you can use them the same way you would use an army with a special unit. The difference is that you cannot control where these units appear and you cannot embbed them into your armies or add troops to them. Every player gets up to three travelers and every statue of Zeus that you build in one of your cities will bring you one extra traveler. If a traveler is killed, you will get a new one on the next day.
Colonist: With the help of the colonist you can approach enemy cities and convince some of its citizens to join your side.
Thief: A thief will steal some of the gold of an enemy city for you.
Gold Seeker: Der gold seekers diggs in the mountains looking for gold, that he will bring back to the city. The further away from the city, the more he finds.
Crystal seeker: they spend their time looking for salt crystals in forests. The further away from the city, the more they can find.
Farmer: The farmer can be used to claim some of the enemys resources for yourself.
Saint: The saint has an unusual effect on the legions in his vicinity: their numbers will grow with time and reach up to 999 troops in every legion.
Trader: The trader can do small commerce and trade goods for you with enemy cities. He's an honest, law-abiding traveler, respecting the principles of the free market, so he won't steal anything. You have to bring him back to one of your cities to claim the profit from the traded goods.