In 1624, the Dutch Republic incorporated much of the current New York City area into the colony of New Netherland. In 1636, as the Dutch were expanding outward from present-day Manhattan, Dutch settlers founded the town of Achtervelt (later Amersfoort) and purchased around Jamaica Bay. Amersfoort was centered around the present-day intersection of Flatbush Avenue and Flatlands Avenue. The Dutch also founded a trading post on Bergen Island, which they renamed "Mentelaer's Island". Ownership of Bergen Island was granted to John Underhill in 1646, and Underhill soon sold the property to others. New Netherland became British New York in 1664, and Amersfoort was renamed Flatlands. Bergen Island, as well as nearby Mill Island and Barren Island, were part of the Town of Flatlands. A settler named Elbert Elbertse bought Bergen Island in 1665, and by the 1670s, all three islands were leased by Elbertse. When he died in 1686, he bequeathed of the island to his son.