It is one of the most relevant fortifications of the region.
El castell de Bairén, also known as Sant Joan, is located 3 kilometres north of Gandia, at the easternmost tip of Mondúver mountain ranges. It is situated at the top of a mountain 106 metres high, from where you can see a wide area that includes the long stretch of coastline framed between Cullera and el Montgó.
It is a place populated since ancient times as evidenced by the archaeological remains dating from the Bronze Age, from the Iberian, Roman and medieval periods, both Islamic and Christian. According to the opposing ceramics, the first moments of the Muslim occupation can be traced back to the Caliphate period (10th century), when the castle was probably built as part of the policy of strengthening the coasts of this area. From the second decade of the 11th century, when the arise of the new taifes, born as a consequence of the disappearance of the Caliphate of Córdoba, the castle regained real importance due to its strategic location with a very wide visual control.
At the end of the 11th century, the first known written reference to Bairén was made, the History of Roderici Campidocti, an anonymous 12th century manuscript describing a supposed battle between Christian troops of Cid and Pedro d’Aragó against the Almoravid army. In the middle of the 12th century, we will find the castle again in a work by Al-Idrisi, a geographer from Ceuta, and in the work of another Arab author who emphasises the importance of Bairén as a station and stop of the coastal route. The Christian conquest is described in la Crònica o Llibre dels Fets (Chronicle or Book of Acts) of el Rei Jaume I, which provides us with the richest and most valuable information about the organisation and structures of the castle at the end of the Islamic occupation. It was built in August 1239 and with Bairén the castles of Palma, Borró, Vilallonga and Vilella were handed over to him.
In 1399, Martí l’Humà named Alfons el Vell the First Duke of Gandia. At this time the castle was already abandoned, however the hermitage of Sant Joan is built, with religious functions and surveillance on the coast threatened by pirate looting. On 15th of July, 1475, the Catholic Monarchs granted Andrés de Cabrera and his wife Beatriz de Bobadilla the castle and the town of Gandia. This act indicates the total loss of importance of the castle, since these are the first owners who did not belong to the royal family. The Borja period began in 1485, when the hermitage was mentioned and referred to. In the 16th century, the castle will be called Sant Joan because of the hermitage that displaces the ancient name of Bairén. In the 17th century the castle was in ruins. At the end of the 18th century the cult in the hermitage was suppressed. (Source: Pérez-Olagüe)