The ancient castle of Rosalcazar is a military architecture that is part of the Oran’s defensive system, in Algeria. His structure was built in the sixteenth century by Diego de Vera, and it reflects the approaches of the Spanish fortification of the reign of Ferdinand the Catholic. These constructions were increased with later alterations, until their consolidation during the term of the governor and engineer Juan Martín Zermeño. The architectural ensemble represented an interesting evolution of the Spanish fortification since the beginning of the sixteenth century until the middle of the eighteenth century, preserving each extension of the elements of the prior period that they are shown in the heritage ensemble of maximum interest.