The St. John the Baptist Fortress is located in the Berlenga Island, its construction was ordered by D. João IV in 1651 and it was concluded in 1656. Built to prevent the island occupation by the North African corsairs or greater enemy powers, it survived until June 1666, when the most remarkable war episode of its history took place.
In this occasion, a Spanish squad, composed by fourteen vessels and a caravel, commanded by D. Diogo Ibarra, beset the St. John Baptist fortress. A small guard, with less than twenty men, and depending only on nine artillery pieces, defended this fortress bravely. The Guard under the command of corporal Avelar Pessoa, managed to resist during two days to the fierce enemy assault, as well as inflict important losses to the enemy forces, translated into a large number of casualties, a sank vessel and two other highly damaged vessels, suffering only one casualty and four injuries.
The depletion of the resources and ammunition, and the flight of some soldiers, exposed D. Diogo Ibarra to a dramatic situation in the Portuguese defence, and culminated in the S. João Baptista Fortress surrendering.