Iron shield boss with leather remains

Iron shield boss: diam. 18cm, height 9.5cm. Large boss with curved dome surmounted by a spike with an iron button 2.2cm diam., slight carination at sides above a sloping waist and a broad flange width 2.5cm. Originally there were five broad disc-headed rivets around flange, diam. c. 2cm, with shanks length 1cm. One has a diamond-shaped bronze washer at its end. Traces of leather adhering to underside of flange. Flange recently damaged.Sarre or Bifrons.