Viking Round Brooch, 10th century, Birka, Uppland, Sweden. 900-1000AD Small circular bronze brooch used by women to fasten the neck of their linen underdress. Classified as Jansson's Group 4B of cast brooches, decoration of four volutes and pseudogranules, imitating filigree work. Found at Birka in grave 762...A small loop on the rear is for hanging utensils or ornaments. Dia 2.7 cm Bronze or brass, iron pin
This is actually much more recent than Viking. 15th-17th c. I believe. "Huge Viking bronze brooch, c. 8th-9th century AD. Comprised of a large, flat disc with notch and pin. Round incised details around the front surface. Great copper-green patina. Big 43 mm (1 5/8") diameter. Found in Latvia"