Abstract Based on information board data, the Fort Oranje Ternate founded in the year 1607. It was 412 years old, where Fort Oranje constructed by masonry with main materials of the coral river and coast marine with lime mortar. However, Fort Oranje at the south side was collapsed on August 24th, 2017. This research is to study the collapsing problem of the fort construction, authors were investigated in field and found a collapse area about 24 meters in length, and 5.7 meters in height. In visualization views show that fort construction failure due to internal stability indication. Therefore, to measure the physical and chemical parameters of Fort Oranje construction for calculation, authors are taken some mortar samples in the field, and bring it into laboratories. In which, mortar samples have to observe the quality by using a compression machine in Structure and material laboratory, chemical contents analyzed in the Chemical laboratory. Finally, the results of the compressive test machine for lime mortar are found on average about σ t ′ of 1.2 MPa and it is less than 19,9 MPa for normally mortar material with cement. Geometrical fort existing consisted of width at top b 1 of 0.70 m, width at bottom b 2 of 1.20 m, the total weight of masonry W of 108.3 kN. Then, soil fill parameters such as bulk density γ s of 17.2 ~ 19.2 kN/m 3 , internal friction φ s of 16.5°, cohesion c ≈ 0, and height h r of 3.26 m. Finally, simulation results for height h k = 3.26m ~ 3.9m are obtained factor of safety for overturning Fs1 < 2.0, Meanwhile, a factor of safety for sliding Fs2 at the base are found Fs2 of 1.43 ~ 1.53. Moreover, Chemical content analyzed by XRF test method for the lime mortar sample is obtained by dominating Calcium Oxide (CaO) of 78.81%.