The Palace of the Dey at Algiers is located inside the Citadel of Algiers which was built in the 16th century (1516) by ‘Arrudj (Barbarous). The citadel is located at the higher part of the city and was the first military building at that time. The citadel was the janissary barracks and initially contained a powder keg, a walk, Janissaries residence places and their mosque. Starting from the 18th century appear new constructive strata. In 1716 some part of this military edifice was destroyed by an earthquake. In 1783 the Spanish bombarded Algiers and a bomb fell into the first storey of the palace. The architectural transformations took place in 1817 when the Dey ‘Ali Khūdja lived at the janissary’s barracks. Thereafter and during 12 years several buildings were added to this whole defensive structure as the second and the third floors of the palace, the Dey’s mosque, the bath, the Bey’s palace and the winter garden. During the French colonization, the palace undergoes other transformations as the destruction of most of the rampart of the city contiguous to the palace which caused its instability and which until today accentuates its vulnerability. The lack of maintains, the abandonment and the bad restoration which took place during the 20th century increased this vulnerability. This work based on a visual screening will present the various aspects of vulnerability due to static weaknesses of the angles and absence of wind-bracing of this palace.