Thornbury is situated right in the heart of the Lower Severn Vale. The Borough of Thornbury was established by Charter in 1252 AD by Richard de Clare, Earl of Gloucestershire and Lord of the Manor of Thornbury. The earliest surviving features of the medieval Borough and Town are the layout of the streets, lanes, and burgage plots along with their associated paddocks and orchards behind the walled gardens of the burgage holders' houses.

The principal streets, High Street, Castle Street, St. Mary Street and John Street, are lined with predominantly 17th and 18th century facades. Often the structure behind them is of an earlier date. The buildings are constructed from local stone and roofed with locally made red pantiles. The combined effects of stone boundary walls, rendered building facades, varied roof levels and the unified scale of the buildings of the old town create its special character.

In the High Street, the prominent Market Hall was the focus for the cattle market held in the High Street until it was moved to Rock Street in 1911.