Fort Saint-Jean

"The highest ranking man I've seen is a teniente (lieutenant). He's lightly protected, but the fort is so big, we'll need to be smart to find him."

- Élise warning Aveline about the fort's size, 1768.

Fort Saint-Jean, known as Fort San Juan del Bayou under Spanish rule, was a fort located in the Louisiana Bayou. Built in 1701 by the French, before the city of New Orleans had even been founded, the fort served to protect the important trade route along the bayou.

History
After Louisiana came under Spanish control in 1763, the original fortification, which had become neglected, was rebuilt using masonry and brick. A lighthouse to guide the ships was also added.

In the pursuit of Templar interests, governor Antonio de Ulloa used the fort to house kidnapped slaves that were to be sent to the work site of Chichen Itza, Mexico. The Assassin Aveline de Grandpré discovered this practice in 1768 and subsequently infiltrated the fort with her smuggler ally Élise Lafleur to shut down its operations.

Three years later, Aveline would return to the fortress to disable its lighthouse, sabotaging the plans of a Templar named Vázquez, who intended to divert a supply ship for his own purposes.

Decommissioned in 1823, the fort was turned into an amusement park roughly 60 years later, a purpose it served up until the 1920s.

Reference

 * Assassin's Creed III: Liberation