aerial photograph of the Cow Tower Norwich , Norfolk, England UK. The Cow Tower is a medieval artillery tower built to defend Norwich from attacks from the North East over the River Wensum. Its an unusual construction as it was never part of the city walls but intended to serve as a stand alone defence like a mini castle.The tower was heavily fought over during Kett's Rebellion of 1549 but although it suffered damage from incoming cannon fire, it held firm.