Fectio was a Roman castellum in the province Germania Inferior established in the year 4 or 5 AD. It was located at the place where the river Vecht (Fectio) branched off from the Rhine, leading to Lake Flevo, which was later to become the Zuiderzee. This was near the modern village of Vechten in the municipality Bunnik, Utrecht, Netherlands.
Under emperor Claudius, Fectio became part of the Limes Germanicus. The archeological site contains the remains of a fort, port, cemetery, and a civilian settlement. In 1995, it was submitted to be a World Heritage Site and is currently on the tentative list.