Pot rim, hand-made ceramic. Similar pots have been found e g in Varbola, Pöide, or Soontagana hill-forts.
Literature:
Tvauri, A. (2005). Latest Iron Age Pottery In Estonia (from the 11th century to the middle of the 13th century). – Muinasaja teadus, 16. Tartu-Tallinn, 72-78. Read the article (ENG p. 161-163): here.