The building of the South Wales Railway in the 1850s was responsible for the decline of many of the small ports along the Bristol Channel coast, and St Clears was no exception. The railway passed about two miles north of the castle, and new building at the north end of the High Street spread eastwards along Pentre Road, and then northwards to the station. Pentre Road is now the main commercial centre of St Clears and was formerly part of the A40 road until the bypass opened.