Site of a battle between Teutons under Arminius and Romans under Germanicus. The latter had led his troops over the sea to the river Ems and further on land via the river Weser in the summer of AD 16. The Romans won the battle in the I. plain (campus) between the Weser and hilly terrain (Tac. Ann. 2,16,1) I. cannot be localized but is generally assumed to be in the surroundings of Porta Westfalica.
B. Rappaport, s.v. I., RE 9, 903-905
E. Koestermann, Die Feldzüge des Germanicus, in: Historia 6, 1957, 429-479, esp. 425-455.