It seems fairly certain that the founder of Sennen in Cornwall was in fact an Irishman, St Senán (Old Irish Senán, pronounced ‘shay-nawn’) mac Geircinn (c.488-544). His name means "little old wise man" in Old Irish and it is thought that he may have been named after an earlier river god whose name gave rise to that of the River Shannon. He was a stepbrother (via his mother) of the female monastic founder St Conainne and was born in 488 in Moylough, near Kilrush, Co.Clare, in the West of Ireland. According to the prose life, his mother entered labour while walking through the woods; when she grasped a tree branch for support, it is said to have blossomed to foretell the virtues of the saint.
Senán promised his life to God when still a boy, after a miracle where a path opened for him and the cattle he was driving across an estuary at high tide (a hagiographical allusion to Moses and the parting of the Red Sea and to Senán’s prophetic leadership skills). He studied in many monasteries in Ireland, including Glendalough and Kerry, notably under the monk Cassidus, from whom he received the habit and tonsure of a monk. Cassidus sent him on to St Natalis at Kilnamanagh, whereupon completion of his studies he was ordained a priest; he later became the first bishop of his main foundation, the monastery on Inis Cathaigh / Scattery Island in the estuary of the river Shannon, near Kilrush the area of his birth, which he founded c.534. Early Christian earthworks and medieval buildings survive.
Senán began his missionary career by founding an abbey on Inishmore (or Deer) Island, leaving St Liberius to preside over it, and a church in 510 (or 512) at Templeshannon (Teampul Senain – ‘Senán’s Church’), near Enniscorthy, Co. Wexford, an area that has early links with Cornwall. From there he set off on pilgrimage to Rome via Britain, where the Latin verse and prose Lives say that he founded two churches in Cornwall, and give him associations with St David of Wales, whom he visited on his way back to Ireland. The date for his stay in western Britain is 520 and he was back in Ireland by 521. That means that Sennen Church is one of the few in Early Christian Cornwall to have a precise foundation date - 520. Senán would have left a follower to head the monastic community he had founded here.
Senán would have sited his mission in what was to become Sennen on account of its importance as an international trade hub and because it was already a centre of population. The prehistoric and Roman remains from the vicinity bear this assumption out. Whilst the church is situated in their midst, on the clifftop plateau, there is evidence for a chapel being established by him close to the beach, where fishing and trading were a focus. Records refer to an ancient Chapel Idné, or ‘Narrow Chapel’ which was 45 feet long by 16 feet wide and was latterly used as a home, which still survived in the late 19th century. It is thought to lie near where the surf shop in Sennen Cove beach car park now lies, commemorated by its stained glass window depicting a Celtic Cross, but it, or parts of it, may still survive between the public toilets and the houses lining Sennen Cove Rd, where tracery remains in a narrow chancel-like stone structure which could even be a chapel. Such a cove-side site fits the profile of early hermitages founded by early Irish and Welsh saints, as found at St Govan’s Chapel, Pembrokeshire, and at nearby St Levan with its baptismal well-chapel and beehive hut foundations on the cliffside above the beach.
Senán had sailed from the South East tip of Ireland after visiting St Maedóc of Fearns, again as recorded in the Latin prose version and the Irish version of his life, and stayed for a while in Tours (his tutor, St Finian, had studied in Martin of Tours’ monastery). His cult in Gaul is said to have arisen from this visit. Senán was also revered in Brittany, where his name is recorded as Sané, with his cult centre at Plou Sané (Plouzane, ‘the Church of Senán’).
Senán is noted for protecting and healing eyesight. In preparation for his battle with a sea monster, the Cathach, the archangel Michael transported Senán to the highest hill on the island, to survey the territory for it. St Michael is renowned for fighting evil in high places – St Michael’s Mount is named for him on account of some fishermen in peril at sea during a storm in the 495 who saw him battling Satan on the mount and were saved. This may explain a little-known local feature near Sennen, which is that, until around 1900, the southern slope of Chapel Carn Brea (the first and last hill in Britain) may have been the site of an early Celtic monastery. Its beehive huts would have resembled those that still exist on the famous Skellig Michael, off the SW coast of Ireland, which was in turn modelled upon the monasteries of the desert fathers, such as the Coptic St Anthony’s in Egypt. Chapel Carn Brea’s stone huts were cleared for building materials, but some traces remain in the bracken and in old photographs.