Pau was a castelnau founded at an unknown date, in the second half of the 11th or the very beginning of the 12th century, to control a fording of the Gave de Pau which was used for the passage of the shepherds in transhumance between the mountains of Ossau and pasture of the plain of the Pont-Long. A castle was built, overlooking the north bank, at equal distance from Lescar, seat of the bishops, and from Morlaàs, capital of the Viscounts of Béarn.