Atlit fortress was built during the Fifth Crusade in the early spring of 1218 by the Knights Templar and named Castrum Perigrinorum (Pilgrim Castle). The fortress is located just 15 km south of Haifa, perched on a sea promontory, and commands the coastal route. It stands isolated by two massive walls, the inner towering over the outer, creating a barrier between the fort and the coast. The outer wall was approximately 15 m high and 6 m thick with three square towers, and an inner wall with two 34-m-tall square towers. Between the walls, there was a ditch carved at sea level into the bedrock. The fortress endured continuous destruction, beginning with being partially dismantled by the Mamluks, and suffered severe damage during the Galilee earthquake of 1837. Additionally, it was further damaged by Ibrahim Pasha in 1840, as he used it as a source of stone for Acre. After the demolition, the inner wall remained intact on the first floor, and a 10-m section of the second floor. However, it has considerable damage due to prolonged exposure to environmental conditions such as capillary rise, daily winds carrying sand and seawater, high temperatures, moisture, salts, and deliberate destruction. Conservation issues arise from the sustained deterioration of Kurkar sandstone due to environmental conditions, causing varying levels of disintegration in bonding materials and stones. The conservation measures aim to prevent the inner wall from deteriorating by using hot mix mortars to restore the core and stabilize the inner wall vault structure. The project findings show that suitable hot-mix mortars effectively and sustainably protect the inner wall structure from destruction and changing weather conditions compared to other mortars based on lime putty or Natural Hydraulic Lime NHL. Stabilizing the wall structure depends on understanding the ancient application of building technologies, mortars, mixture techniques, and additive reactions with integrated monitoring.