Fort Mercer

Fort Mercer is a location in the Río Bravo region of the New Austin territory. Fort Mercer is associated with an outlaw hideout, and the location of Bill Williamson.Fort Mercer also might have been a fort used during the mexican american war as it is near the border with mexico

Fort Mercer is an important storyline location, as it is here that Williamson remains protected in the fortifications, alongside his outlaw companions.

Storyline
Marston seeks out Williamson to appease the demands of Agent Edgar Ross, and during a verbal confrontation where Marston appeals to Williamson to surrender, Marston is severely wounded. After rescue and recovery, thanks to Bonnie MacFarlane, Marston starts to organize a raid on the fort. Marston's plan requires the assistance of various characters: Marshall Leigh Johnson, Nigel West Dickens, Irish and Seth Briars. Each character offers different resources and abilities for Marston to complete his mission:
 * Marshall Johnson provides his skills as a veteran gunfighter, as well as the services of his deputies Jonah and Eli.
 * Nigel West Dickens arranges an armoured stagecoach to assault the fort.
 * Seth Briars provides a unique distraction for outlaws guarding Williamson.
 * Irish supplies Marston with a mounted machine gun.

Singleplayer
After Williamson has been cleared from the fort, it is avalible as a standard gang hideout later on.

You must meet a Gunslinger outside the walls, at which point he will vault you over the wall. You must then climb up, kill several enemies, drop down and open the front gates for him. After this, you must simply kill all remaining enemies in Fort Mercer, resulting in the 3 Gang Leaders (enemies with slightly more health than regular ones) will burst out of the treasure room. Dispatch them, and go grab roughly $300 in treasure! The hideout is complete once the Gunslinger enters the treasure room too.

Occasionally, the Gunslinger will get stuck behind a wooden rack-like object leaning against a wall. Simply run into this object to make it fall over and he will continue on.

Multiplayer

 * In multiplayer free roam, the LeMat revolver is located here. Also a Mounted Machine Gun is located up top on a roof, You can use it for when your in a "Bad" spot.

Achievements
Fort Mercer is associated with several hideout achievements:
 * Instinto Asesino: Complete Fort Mercer and Nosalida Hideouts in Single Player.
 * Slow on the Draw: Get 10 assists in a single Hideout in a public Free Roam session.
 * Have Gun Will Travel: Complete all Hideouts in single public Free Roam session.

Trivia
Fort Mercer is a real fort that was made during the American Revolution. It sits on the banks of the Delaware River and was headed by George Washington. In-game the Fort is used by Bill Williamson.