In the Courts of the Crown of Aragon held in Monzón (Huesca, 1528) it was raised the need to organise the coast defence of the Kingdom of Valencia through a series of fortification works and the creation and maintenance of militias in order to avoid the attacks and incursions of the Turks and the Berber corsairs. In Alacant (1533), under the auspice of the Duke of Calabria, viceroy of the Kingdom of Valencia, and the design of Joan de Cervelló, noble, military and engineer of King Carlos I and with great experience in artillery and fortification of cities, three bastions were built taking advantage of the medieval walls: Sant Francesc, Sant Bertomeu and Sant Sebastià. These improvement works on the walls continued with the rise of two more towers that protected the gate (Puerta del Mar or Montserrat). The bastions had a circular plan and an escarp elevation up to their half and vertical until the crowning, besides a low armed parapet. They were demolished because of the urban renovations that Alacant experienced during the nineteenth century. However, the historical planimetry, engraving images and photographs, as well as the archaeological excavations carried out in them allow to know their morphology and materials, which are explained in this paper.