Fort Winthrop, built in 1808 and named Fort Warren until 1834, was a defensive fortification in Boston Harbor named after John Winthrop, an early governor of the Massachusetts Bay Colony. The fort was built on Governors Island, which was named Conant's Island until it was granted to Winthrop in 1632. His family owned the island until 1808, when the U…Fort Winthrop, built in 1808 and named Fort Warren until 1834, was a defensive fortification in Boston Harbor named after John Winthrop, an early governor of the Massachusetts Bay Colony. The fort was built on Governors Island, which was named Conant's Island until it was granted to Winthrop in 1632. His family owned the island until 1808, when the United States acquired land in the center of the island for the construction of a fort under the Second System of US fortifications. Between 1808 and 1812 the government built an earthen fort on that land, in the form of an eight-pointed star. Sylvanus Thayer, later famous as Superintendent of West Point, was in charge of the fort's construction. Secretary of War Henry Dearborn's report on fortifications for December 1811 described it as "...a star fort of masonry, mounting twelve guns...and brick barracks for 40 men...On the West head, a circular battery of ten guns mounted on the South point, a circular battery, calculated for ten guns...".