Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Fort Halifax was a U.S. colonial outpost on the Kennebec River at modern-day Winslow, Maine. It is a National Historic Landmark. Fort Halifax was a fort on the north bank of the Sebasticook River. Its blockhouse, which survives, is the oldest blockhouse in the United States. It was part of a garrison built by the Province of Massachusetts Bay in 1754-1755 at the outset of the French and Indian War.