Between 1778 and 1780, Polish engineer and military hero Tadeusz Kościuszko oversaw the construction of the garrison's defenses. Kościuszko's small garden retreat still stands today as Kosciuszko's Garden. The Great Chain and high ground above the narrow S curve in the Hudson River enabled the Continental Army to prevent British ships from sailing up river and dividing the Colonies. Because of the unique bend in the river, ships of the day had to slow down to a near complete stop to navigate the turn. Though never tested, the chain performed its purpose by preventing British movement up river. Several forts and redoubts were constructed to defend this turn in the river. The closest to the river was Fort Clinton, formerly named Fort Arnold for his victory at Saratoga in 1777. The remains of this fort can be seen on the western edge of the Plain between Thayer Road and the Hudson River. A few hundred feet higher in elevation was Fort Putnam, near the site of the present day Michie Stadium. A series of smaller redoubts protected these two forts. Several are still visible, including Redoubt Four, at the highest point on the academy, and Redoubt Seven, across the river on Constitution Island. It was as commander of the fortifications at West Point that Benedict Arnold committed his infamous act of treason when he attempted to sell the fort to the British.