Monmouth is located in an area of Devonian old red sandstone, at the point where the River Wye is joined by its tributary, the River Monnow, and immediately north of the point at which the smaller River Trothy flows into the Wye from the west.
In climatic terms, the town is located between those areas around the Severn estuary which show a maritime influence, and the cooler and drier conditions of the Midlands of England further inland [REF].