Saint Brendan’s Isle, also spelled St Brendan’s Isle, is a phantom island, or mythical island, supposedly situated in the North Atlantic somewhere west of Northern Africa. It is named after the Saint Brendan who founded the Clonfert monastery and monastic school. It is said to have been discovered by the saint and his followers while they were traveling across the ocean, evangelizing islands. It appeared on numerous maps in Christopher Columbus's time, most notably Martin Behaim's Erdapfel of 1492. It is referred to as La isla de San Borondón or isla de Samborombón in Spanish.
The first mention of the island was in the ninth-century Latin text Navigatio Sancti Brendani Abatis (Voyage of Saint Brendan the Abbot), placing the island into Irish and European folklore.
This island is named after Saint Brendan, who claimed to have landed on it in 512 together with 14 monks, with whom he held a Mass. The monastic party reported its stay as 15 days, while the ships expecting their return complained that they had been kept waiting a year, during which period the island remained concealed behind a thick curtain of mist.
In his Navigatio Sancti Brendan Abbatis, the monk Barino mentioned having visited this same "Paradise" in the Atlantic, a thickly wooded mountainous island where the sun never set and it was always day: the flora were abundant, the trees bore rich fruit, the rivers ran with fresh water, and the birds sang sweetly in the trees.
In Planiferio de Ebstorf (1234), Marcos Martinez referred to "the lost island discovered by St Brendan but nobody has found it since" and in Mapamundi de Hereford (1275) the whole archipelago is described as "The Isles of the Blessed and the Island of St Brendan".
The Portuguese writer Luís Perdigão recorded the interest of the King of Portugal after a sea captain informed Henry the Navigator (1394–1460) that he had found the island but was driven off by tumultuous sea conditions. Henry ordered him back: he sailed off but never returned. Christopher Columbus is said to have believed in its existence.