For 10 points, name this river that defined the boundary of the Roman empire along with the Danube.
The Fossa Drusiana connected Flevum to this river. Gnaeus Domitius Corbulo constructed his namesake canal southward from this river into an estuary to save ships a trip on the sea. This river, on which the city of Mogontiacum was founded, bounded the Agri Decumates to the south and west. Two pairs of wooden piles were driven obliquely into its riverbed with a winch, then protected with further pilings upstream, in a feat of military engineering. A Roman army subdued the Ubii by building a 300-foot (*) bridge over this river in ten days and demolishing it eighteen days later. The upper part of the Germanic limes is defined by this river, cities along which include Colonia Claudia Ara Agrippinensium, or modern Cologne. For 10 points, name this river that defined the boundary of the Roman empire along with the Danube.
The Fossa Drusiana connected Flevum to this river. Gnaeus Domitius Corbulo constructed his namesake canal southward from this river into an estuary to save ships a trip on the sea.
Rhine River [or Rhenus]