St. Mary Street (Heol Eglwys Fair) and High Street (Heol Fawr) are major commercial streets in the Castle Quarter of Cardiff city centre, Wales, which form a major north–south thoroughfare in the centre. High Street begins at the junction of Castle Street on the A4161 and ends at the junction of Church Street and Quay Street, from where St. Mary Street begins until the roundabout at Callaghan Square on the A4160.