Historically, the term Césares (Caesars) was used to denote a city of unknown location. Similarly, Patagonia itself was given the name Incognita.
As with many stories of fantastical cities in South America at the time, the staple of the City of the Caesars was its troves of gold, silver, and diamonds. The nature of the city was often thought to be mystical, only appearing at certain times or causing outsiders to forget any visit there upon leaving.
The city itself was thought to be in a valley in the Andes mountains, somewhere between Chile and Argentina. It was occasionally said to be situated between a mountain of gold and a mountain of silver.
The inhabitants of this city were often disputed. Proposed residents include Patagones, ghosts, and survivors of either the Inca Empire, a wreck in the Strait of Magellan, or the Battle of Curalaba. However, the most common claim is that it was inhabited by white people without specification as to their origins.
Based on its location and descriptions, the City of the Caesars may simply be a misconstrued explanation of the Peruvian Empire. Another common theory is that local populations directed Conquistadors to the city in order to get rid of them, knowing full well it didn't exist.
More recently, an abandoned fort in Argentina has led some to believe that the city truly did exist, and that its founders were members of the Knights Templar. Supposedly, the fort was home to the fabled Holy Grail.