Starting in the Renaissance era, Spies will become available. You may earn Spies from certain technologies and civics. They can be built in any city, but they cannot be purchased with Gold or Faith. Spies begin at the Recruit level, and may gain levels from successful offensive operations, or capturing an enemy Spy. Upon reaching level 2, Spies may also earn promotions.
Spies are not moved like other units. They jump from city to city using air, sea, road, or foot travel, each with their own travel time, but they may not move to an ally's city. Once established in a city, a Spy can be sent to a specific district and begin their mission. Missions include stealing technology boosts, creating rebel units, or simply increasing diplomatic visibility. Each mission takes a certain amount of time, and will have a different outcome. Your Spy may be killed or captured, or maybe he failed his mission but was not detected, or perhaps it was not detected and the mission was a success.
Every civilization can produce 5 Spies. Play as Catherine to earn the ability to produce 6.