The land of Evol was ceded in 957 by the Count of Cerdagna, Sunifred II to the abbey of Santa Maria of Ripoll. Before 1230 it belonged to Bernard I of Alion, and then to his son Bernard II who was burned at the stake by the Inquisition in 1258. King James II of Aragon named his son Guillem of So, Lord of Evol, and it was he who in 1260 built the feudal castle near the new frontier line with the kingdom of France (treaty of Corbeil in 1258).
The castle, built on a buttress of Mount Coronat, has a quadrilateral shape, the walls being about 40 metres long with a round tower at each corner, and a round keep in the middle of the north wall. The residential building occupied the western wall and consisted of three connecting rooms. The east and west walls had a postern, the main entrance being through the southern wall. To the west lies an outdoor terrace (the miranda) overlooking the valley. There was an upper floor on the level of the walkway.
As early as 1343, Viscount Jean de So had a new castle built near Olette (The Bastide) which was to become his residence. The old castle would now only house a small garrison, and served as a storehouse for the farmers-general. It was sold off as a national property in 1812 and remained in private hands until 1990 when it was bought by the municipality of Olette-Evol.