Thuin (French pronunciation: [tɥɛ̃]) is a Walloon municipality located in the Belgian province of Hainaut. The Thuin municipality includes the old communes of Leers-et-Fosteau, Biesme-sous-Thuin, Ragnies, Biercée, Gozée, Donstiennes, and Thuillies.
This area was already used as a burial place in Gallo-Roman times, around the 2nd and 3rd century. The earliest name of the settlement, Thudinium Castellum, referring to a Roman fortification, is found on a 9th-century offering in the Lobbes abbey, which lists various neighbouring towns and related tithe duties. The village was a possession of the abbey of Lobbes and, together with the abbey, became part of the Bishopric of Liège in 888. The neighbouring Aulne Abbey, reputedly founded in the 7th century by Landelin, a repentant robber, was also made part of the Bishopric of Liège.
A century later, Prince-Bishop Notger had a defensive wall built in Thuin, which then became the westernmost of the 23 bonnes villes (or principal cities) of the bishopric.