Pistyll Dewi holy well is closely associated with Capel y Pistill (NPRN 305400), the site of a documented pilgrimage chapel to St Davids: a late 16th century source describes the chapel as being named for a spring that ran under it into a cistern at its eastern end. The site is immediately west of the River Alun, some 200m north-west of where it joins the harbour at Porthclais. The port (NPRN 34342) is mentioned in the Mabinogion and the old harbour wall, thought to have been built by the Romans, is largely intact. The stone well chamber is set upon a platform on a hillside. Measurements are given as 0.8m by 1.3m high. The well is associated with a circular cropmark identified on aerial photographic coverage and suggested to represent the southern arc of a chapel enclosure with a diameter of some 45m.

Sources include:
Cambria Archaeology, 2003, Early Medieval Ecclesiastical Sites Project, Pembrokeshire gazetteer

N Vousden, 30 October 2018