On June 24, 1664, the Duke of York sold the portion of his large grant that included present-day New Jersey to John Berkeley and George Carteret for a proprietary colony. The land was not yet in British possession, but the sale boxed in the portion of New Netherland on the West side of the Delaware River. The British conquest of New Netherland began on August 29, 1664, when New Amsterdam was coerced to surrender while facing cannons on British ships in New York Harbor. This conquest continued, and was completed in October 1664, when the British captured Fort Casimir in what today is New Castle, Delaware.