Castell del Rei, Rock castle in Pollensa, Spain

Castell del Rei is a rock castle perched on a crag in the Sierra de Tramontana at roughly 492 meters elevation. The structure consists of stone walls and ruins that overlook the valleys and terrain of northern Mallorca.

The site was already used as a fortification in Roman times. In the Muslim period it held out with the Castle of Alaró as the last stronghold against the troops of James I of Aragon, who invaded Mallorca in 1229; the defenders resisted until March 1231. In 1343 it was again a last refuge, holding out for three months of siege for James III of Mallorca after Peter the Ceremonious had annexed his kingdom.

Locals call it "U castell d'u rei" in the Pollençí dialect. The poet Miquel Costa i Llobera wrote the poem "Castell del Rei" in 1896, and the site is listed as a Bé d'Interès Cultural.

Visiting requires permission to cross the private Valle Ternelles estate where the castle sits. Local adventure companies organize guided hikes that handle access logistics and provide safe routing through the terrain.

The name survives in Pollencí oral speech as "U castell d'u rei". In 1896 the Pollença poet Miquel Costa i Llobera wrote a poem titled "Castell del Rei" about the site, and the ruins stand on the mountain of the same name at 492 m, above the Vall de Ternelles.