Fort Nassau – South River – was built by the Dutch West India Company on the Delaware River at the mouth of Big Timber Creek, near present Gloucester, NJ. It was described by settlers as a “factorij” which was basically an early form of free-trade zone, set up to trade fur with the Native Americans.
For the first 8 years of its history, the fort was inhabited intermittently by the Dutch in seasonal migrations. But due to this, English Colonists from Virginia occupied the fort in 1635, after which time the Dutch retook the fort by force under the governor, Wouter van Twiller. This activity was the first armed conflict between the English and Dutch in the New World. After that, the fort was continuously manned, although the fort turned out to be ill-suited to the fur trade, since the riched fur trapping was on the west side of the Delaware River.
Between 1638-1655, Ft. Nassau and the area around it changed hands – and names and locations – between the Dutch and the Swedes several times. Specifically, in 1651, Dutch Governor Peter Stuyvesant dismantled Fort Nassau and moved it to what is now New Castle Delaware, and renamed it Ft. Casimir. In 1654, Swedish commander Johan Risingh tried to expel the Dutch from the Delaware Vallee by capturing Fort Casimir, and renamed it Fort Trinity.
But finally on September 11, 1655, Peter Stuyvesant led a Dutch force to retake Fort Trinity, and renamed it (again!) as New Amstel. The Dutch then occupied Fort Christiana on September 15th, so all of New Sweden came under Dutch control. The Dutch appointed John Paul Jacquet as governor, and made New Amstel the capital of the (newly) Dutch controlled colony.